Psoriasis is a chronic skin condition with a tendency to relapse. It has many shared features with seborrheic dermatitis and is believed to be a genetically inherited skin condition, triggered by environmental and immunological factors .
Similar to seborrheic dermatitis, it is estimated that 2-3% of world population is affected by the condition . With 25% of these individuals classified as having moderate to severe skin symptoms .
Psoriasis can involve specific areas of the skin (such as scalp) or cover major portions of the body. Commonly affected skin areas include the scalp, finger tips (toes and fingers), palms, soles, belly button, buttocks, under the chest/breast, genitals, elbows, knees, shins, and lower back . Scalp psoriasis is believed to the most common and is seen in roughly 75-90% of individuals affected by psoriasis .
Psoriasis appears to be a skin disease that is directly related to abnormal immune function [6, 7, 8]. And chances of encountering the skin condition increase with age .
Many of the same symptoms as seborrheic dermatitis are often present:
- Patches of skin inflammation
- Silvery scales
- Dry and cracked skin
- Itching, burning, and tingling sensations
But abnormal epidermal differentiation and hyper-proliferation are unique to psoriasis.
Healthy skin is composed of skin cells which take roughly 48 days to develop and mature (being pushed from the bottom to the outside surface). In psoriasis, the rate of skin cell turn-over can be as short as 6-8 days . The skin cells literally generate too fast and this is represented as plaques at the surface of the skin.
In addition to plaques, itch is a main component of the condition and the word psoriasis is derived from the Greek word “psora”, meaning itch.
Abnormal Immune Function and Inflammation
It is proposed that the primary mechanism behind the symptoms stems from defective communication between the innate and the adaptive immune systems .
It has been documented that hyperactive T cells throughout the skin layers trigger local inflammation, activation and migration of additional inflammatory cells, and abnormal skin cell division. Taken together, this process results in the symptoms we collectively know as psoriasis.
Some literature even goes as far as to suggest that psoriasis should not be thought of as a skin condition, but as a systemic inflammatory disorder [2, 11, 12].
Common Issues Accompanying Psoriasis
Physiological factors (itching and burning sensations) of the condition can be quite intense, but many individuals find the psychological effects significantly more severe. The visibility of the condition (by others), results in negative reactions, embarrassment; and this can drastically effect social interactions leading to social withdrawal and depression.
When compared to other chronic health issues (including cancer), only depression and chronic lung disease impaired quality of life measures more then psoriasis .
Metabolic syndrome and cardiovascular disease is present in a high number of affected individuals and can further augment the overall burden of the condition [14, 15]. Individuals affected by psoriasis, should not ignore this aspect of the condition and address these factors pro-actively to avoid more broad health implications.
In addition to depression, metabolic syndrome and cardiovascular disease; several other conditions have been shown to be associated with psoriasis [11, 16]:
- Non-alcoholic fatty liver disease
- Crohn’s disease
Different Types of Psoriasis
Several sub-types of psoriasis exist and these can often overlap.
Accurate diagnosis is important to narrow down treatment options. Although visual inspection of the skin can be a good starting point, visual symptoms are not always precise and a skin-biopsy can help pin-point the specific issue at play.
Plaque psoriasis is the most common form and represents roughly 90% of all cases.
At its core, it involves hyper-production of skin cells and their accumulation on the top layer of the skin. This results in patches of dead skin termed as “plaque”.
Main symptoms include inflammation, skin scales at various locations (size and distribution of scales can vary between individuals) and itchy skin.
Though it is generally not life-threatening, if inflammation covers a large enough area, excessive moisture loss through the skin can be critically dangerous. However, in most cases, life-threatening aspects of the condition are restricted to the side-effects of systemic medication used for treatment .
Plaque Psoriasis = Psoriasis Vulgaris
Plaque psoriasis is also known as psoriasis vulgaris.
Technically a sub-set of plaque psoriasis, it is characterized by inflammation at areas of the skin that flex and/or touch each other. This includes areas such as the armpits, skin folds of the breast, between the butt cheeks, and other areas with similar features.
In inverse/flexural psoriasis, scales are almost non-existent. This is because the friction and moisture of these skin sites prevents their formation.
Scalp psoriasis is essentially just plaque psoriasis that effects the scalp.
The primary characteristic of scalp psoriasis is the intensity of the plaques, which are usually thicker and denser then at other areas of the skin. Additionally, as the hairs grow, the scales can adhere to the hair shaft and cause more pronounced shedding of scales (even in the absence of itching/scratching).
Hair loss (alopecia) can occur if the plaques are allowed to build-up and damage the hair follicle . Luckily, this hair loss is usually temporary and reversible.
Severe Cases of Scalp Psoriasis
If the intensity and density of the scales is severe enough, it may be consider as pityriasis amiantacea .
Erythrodermic psoriasis is a more aggressive form of plaque psoriasis that involves inflammation affecting the majority of the skin surface. In most cases, it appears to be caused by drastic worsening of established plaque psoriasis caused by abrupt stoppage of systemic treatment [20, 21].
Nail psoriasis presents itself as pitting of the nails, yellow or brown patches below the nails and thickening of the skin below the nails.
In some extreme cases, the condition can progress to a point where the top layer of the fingernail (nail plate) can thicken and crumble; leading to loss of fingernails and significant impairment.
Around half (50%) of individuals affected by plaque psoriasis can experience nail psoriasis at some point in their lives . It’s very uncommon for nail psoriasis to present itself without any prior history of psoriasis.
Psoriatic arthritis is a sub-set of arthritis that has been associated with psoriasis. Technically, it’s not a skin condition, but presents itself as inflammation of the joints and connective tissue.
Any joint can be affected, but it’s seen most commonly in the fingers and toes .
Though it only appears in an estimated 0.3-3% of the general population, the chances drastically increase for individuals affected by other types of psoriasis (estimated closer to 10-15%) [24, 25].
In most cases, symptoms are mild and only affect a few joints. In certain individuals, the symptoms can be severe and debilitating; drastically effecting quality of life .
Characterized by scaly tear drop shaped spots which appear on most of the body. In some cases, only isolated skin regions may be effected.
Lesions tend to be concentrated around the torso, thighs, and upper arms. Facial areas such as the scalp, face and ears are also commonly affected, but lesions at these areas are usually not as aggressive .
In the large majority of instances, it appears that guttate psoriasis can be triggered by streptococcal infection and spontaneous resolution can occur [27, 28].
The primary symptom that differentiates pustular psoriasis is pustules (blisters) that produce a white pus. The condition tends to come on strong and during a flare-up, only within a matter of hours, pustules filled with pus can begin to show up on the skin.
Interestingly, in certain cases, pustular psoriasis has been associated with tumor necrosis factor medication and systemic steroid usage (corticosteroids); both of which are treatments commonly used to treat less aggressive forms of psoriasis [29, 30, 31].
Sub-Types of Pustular Psoriasis
Though this type of psoriasis is further broken-down into various sub-sets with finer diagnosis criteria (overlap with psoriasis vulgaris, location of pustules/blisters, degree of pus production, etc), this is outside the scope of this discussion.
Sebopsoriasis is not really a sub-set of psoriasis, but a term used to describe the presence of both psoriasis and seborrheic dermatitis (at the same time). Since it’s a combination of the two conditions, it is usually restricted to sebum rich areas that are common amongst seborrheic dermatitis sufferers.
Common Triggers and Risk Factors
Numerous triggers and risk factors have been seen to be associated with psoriasis. Evaluating each of these more thoroughly can help establish a better understanding of the condition.
Stress and depression have long been known to trigger and aggravate a variety of skin issues; including acne, alopecia (hair loss), atopic dermatitis, seborrheic dermatitis, rosacea and psoriasis [32, 33, 34].
In the case of psoriasis, it appears that emotional stress is one of the most pronounced components of the condition [35, 36]. Some literature even suggest that stress may play a vital role in the initial onset of psoriasis in susceptible individuals .
Though there is no clear-cut evidence that it skin damage can cause psoriasis in the first place, skin with prior damage becomes more susceptible to developing psoriasis symptoms (in psoriasis prone individuals) [37, 38].
Not only is skin injury a potential trigger for psoriasis, it is seen in a variety of other skin conditions. Though not fully understood, this relationship has come to be known as the Koebner phenomenon.
This includes simple skin damage from things such as:
- Chemical irritants
Considering all factors
Sometimes, we overlook the small stuff. For example, certain work environments (such as hair salons, workshops, and production plants) have a high degree of airborne skin irritants and this can result in ongoing damage to the skin barrier and increase the chances of skin issues.
Similar to seborrheic dermatitis, individuals effected by HIV have an increased chance of developing psoriasis . Again, the evidence suggests that HIV itself does not cause psoriasis, but only increases the chance of it’s development in individuals already prone to psoriasis .
Though the relationship is not fully understood, evidence points to abnormal T-cell activity and altered immune function [40, 41].
Certain medications have been seen to cause or worsen psoriasis. Though the underlying mechanism varies between drugs, being aware of some of the more common culprits can help exclude these medication from your list.
Beta blockers are commonly used to treat certain heart conditions; such as hyperthyroidism, anxiety and glaucoma.
In some cases, beta blockers may trigger psoriasis, with the drug propranolol having the most reported cases [42, 43].
However, some contradicting evidence exists. For instance, one team of researchers noted the triggered skin issues may not be psoriasis, but instead a visually similar dermatological disorder ; while others have published evidence that no such relationship exists .
Whatever the case, ruling out beta-blockers may still be worthwhile. In cases where they were responsible for triggering skin issues, clearance has been seen in as little as a several weeks .
Lithium is a medication frequently used to treat depression and mental disorders.
In certain individuals, it can trigger or worsen psoriasis symptoms . Fortunately, the chances of lithium causing psoriasis are fairly small. Yet it’s impact on an already existing condition is significant.
The delay between starting lithium medication and emergence of skin issues can occur anywhere from 20 weeks to 48 weeks after medication has been started. This delay can conceal the relationship and allow it to remain undiscovered while symptoms gradually get worse.
Medication initial developed to combat malaria has also been used to treat psoriatic arthritis and lupus erythematosus (in addition to it’s main purpose as a preemptive measure against malaria).
In several cases, these medications have been reported to severally exasperate existing psoriasis symptoms [id=”114043006,3346150″].
Corticosteroids are commonly used to treat a variety of dermatological disorders (including psoriasis and seborrheic dermatitis).
Though their efficiency is unquestioned, long term usage can have a variety of unwanted effects [49, 50]. In the case of psoriasis, if the long term usage of corticosteroids is abruptly discontinued, psoriasis symptoms may return worse then ever before .
Non-Steroidal Anti-Inflammatory Agents
Various non-steroidal anti-inflammatory medications are often prescribed for a variety of common health concerns which feature pain and/or inflammation. This can range from something as a mild headache, to something more serious such as macular edema (swelling of the eye).
Regrettably, some of these medications have been associated with worsening of psoriasis symptoms  and individuals do not often realize the potential connection .
In many cases, various digestive issues and disorders often accompany psoriasis. This includes things such as inflammatory bowel disease, Crohn’s disease, ulcerative colitis and celiac disease [53, 54].
Some examples of intestinal issues seen in individuals effected by psoriasis include:
- Inflammatory changes in the colon 
- Altered gut microbiota and decrease bacterial diversity 
- Increase intestinal permeability 
Though it is difficult to determine weather or not intestinal issues trigger psoriasis in the first place, it’s likely that some shared underlying immune system deficiencies do exist. And understanding these deficiencies may lead to innovative treatment approaches in the future.
Psoriasis sufferers have been noted to have a low intake of fruits, vegetables, and dietary fiber; combined with a a high intake of refined carbohydrates and fats .
At the same time, some suspect that lipid abnormalities and diets rich in pro-inflammatory omega 6 fatty acids may be directly connected to psoriasis symptom severity [59, 60].
Both smoking and alcohol may increase the chances of psoriasis [61, 62]. Granted, some conflicting evidence exists, the overall consensus is that reducing such bad habits can result in gradual improvement of psoriasis severity.
For alcohol, the most evidence exists for [63, 64]:
- Moderate/high alcohol abuse
- Males more then females
However, since alcohol abuse is a known stress response (some people may turn to alcohol in times of high stress), some have argued that alcohol abuse may simply be a consequence of living with psoriasis and the stress it brings [65, 66].
Whatever the case, in individuals already effected by psoriasis, heavy alcohol consumption is known to worsen symptoms . And in some cases, complete remission of psoriasis has been noted following prolonged abstinence from alcohol .
The negative effects of alcohol abuse on immune function, systemic inflammation, liver function and T-cell activity are all possible mechanisms in which alcohol may worsen psoriasis [69, 70, 71, 72].
The percentage of smokers amongst psoriasis sufferers is significantly higher then amongst the general population. Even if individuals who started smoking after psoriasis are isolated, this relationship appears to hold true .
One paper even suggested that as high as 25% of all psoriasis may been triggered by smoking , but this paper was published in 1993 when nearly 30% of the adult population smoked.
Unfortunately, it does not appear that quitting smoking once psoriasis has already developed has any effect on symptoms .
Plus the overlap between smoking and other poor lifestyle habits (such as alcohol abuse, poor eating habits, low fruit/vegetable intake) leaves a lot of room for uncertainty. Given these overlapping lifestyle habits, how can smoking really be isolated as a single factor [76, 77].
No single explanation regarding the mechanism in which cigarette smoking may influence psoriasis exists. Some possibilities include nicotine’s effect on keratinocyte differentiation  and overall oxidative damage [79, 80].
Similar to seborrheic dermatitis, cutaneous psoriasis and psoriatic arthritis worse in the winter and improve in the summer . Some believe this may be related to the restricted UV exposure and lower vitamin D levels.
Psoriasis Treatment Approaches
Based on the most comprehensive understanding of psoriasis, the majority of treatment approaches aim at resolve symptoms through two primary targets:
- Immune modulation
- Normalization of epidermal differentiation (keratinocytes)
Interestingly, treatments that modulate the immune system, indirectly influence the second target as well. Because of this, these treatments tend to provide more significant relief. But this can be a double edged sword, as treatments that modulate the immune system usually present a larger chance for adverse effects.
In very mild cases, focusing strictly on the second target may prove sufficient.
The most prominent and well documented treatments for moderate psoriasis are corticosteroids and Vitamin D derivatives ; with the most effectiveness seen when a combination of the two is implemented .
Combination therapy is not limited to vitamin D and corticosteroids and has been employed with many of the other treatments. Combining treatments may not only improve effectiveness, but also reduce potential side effects from higher concentrations of a single active agent.
In general, topical therapies usually show effectiveness in as little as 2-3 weeks of use. The first observed improvement is typically the clearance of scales, followed by resolution of plaque and finally by a gradual reduction in inflammation which can take anywhere from 6-8 weeks.
Unfortunately, the potential for side effects and the efforts required to consistently apply many of the topical treatments leaves a lot of room for improvement.
A brief review of the most common topical treatments follows.
Corticosteroids are some of the most commonly prescribed medication for the treatment of various skin disorders. Psoriasis is no exception and corticosteroids are the single most widely prescribed medication for plaque psoriasis .
Corticosteroids do not define a single medication, but instead a category of hormonal medication. The majority of their benefits are attributed to their ability to suppress the local immune response, reduce inflammation and normalize the rate of cell turn-over [83, 84].
Tough particular differences between the various corticosteroids exist, they are typically grouped by potency. The more potent options are known to be more effective, but they also come with an increased chance of side effects .
It is the possible adverse effects that really bring down this treatment approach. Long term usage can result in skin atrophy (also known as skin thinning), development of spider veins at the skin surface, formation of stretch marks, and a variety of other degenerative skin manifestations [86, 87].
Since psoriasis is considered a long term condition that requires ongoing treatment, it’s hard to say weather or not the initial relief outweighs the possible risks.
Vitamin D Derivatives
Synthesized vitamin D derivatives, such as calcipotriene, calcipotriol, and calcitriol, are some of the most effective medically reviewed psoriasis treatments available today. They have been shown to be superior to coal tar, hydrocortisone (considered a potent corticosteroid), anthralin and betamethasone valerate [85, 88].
Vitamin D derivatives work by binding to the Vitamin D receptor of various skin cells and modulating their behavior . The end result is regulation of the skin cell turn-over rate, elimination of inflammatory cells, and inhibition of the T cell triggered inflammation response [90, 91, 92].
Adverse effects have been seen in a small portion of individuals, but their overall safety profile appears to be well documented [93, 94, 95, 96].
Tars are some of the oldest established psoriasis treatments and are also used for various other common skin disorders (including seborrheic dermatitis). In the past, they have been derived from wood and animal source, but coal derived tar has become the most prominent form used today .
Their effectiveness in moderate psoriasis and established safety profile makes them great candidates for long term treatment [98, 99]. But their messiness, strong odor, difficulty of application, and lack of effectiveness in severe psoriasis has lead many in search for other solutions [100, 101].
The beneficial effect of coal tar on psoriasis is not fully understood. One possibility is related to it’s suppressive effect on DNA synthesis leading to decreased rate of keratinization . Other possible explanations relate to it’s anti-inflammatory and antimicrobial properties .
Anthralin is a synthetic medication that inhibits cell growth leading to down-regulation of keratinocyte formation .
It’s effectiveness in psoriasis treatment is well established and even rivals potent corticosteroids, but it’s widespread use remains limited by it’s potential to irritate and stain the skin .
Tazarotene is a synthetic retinoid, which has been shown to reduce inflammation and down-regulate epidermal cell production (reduce the rate of keratinization) .
It’s effectiveness in psoriasis treatment is evident and can be further enhanced by combination with a corticosteroid [105, 106]. Similar to anthralin, it’s adoption appears to be limited due to it’s potential to irritate the skin.
Salicylic acid is a natural chemical found in willow bark. It is now actively synthesized on a large scale for it’s beneficial effects on a variety of skin disorders, including psoriasis and seborrheic dermatitis.
The most common explanation for it’s beneficial effects relate to it’s ability to increase the rate of peeling/shedding of the lop layer of skin, leading to the appearance of healthier/softer skin [107, 108]. Other possible mechanisms of action include it’s antimicrobial and anti-fungal potential, and it’s ability to reduce skin surface pH .
Unfortunately, most studies suggest that salicylic acid alone is not a sufficient treatment for psoriasis and must be combined with other solutions (such as corticosteroids or betamethasone dipropionate) . When used in combination, it has the ability to enhance penetration of other active ingredients; reducing the amount required and improving treatment outcomes.
Controlled exposure to ultraviolet light has successfully been used in many of the most common skin disorders. Numerous studies support the efficacy of both narrow-band (light of specific wavelengths) UVB and broadband UVB therapy for the treatment of psoriasis .
The high clearance rates seen with phototherapy (even in severe cases) have made it a strong candidate for many long term sufferers. However, there appears to be some contradictions in terms of it’s safety profile.
On one hand, there is literature that suggests ongoing PUVA treatment carries an increased chance of photodamage and skin cancer [112, 113]. On the other hand, a 25 year follow-up study on 280 individuals treated with broadband UVB and coal tar (known to make the skin more susceptible to UV damage) failed to show any such relationship .
Whatever the case may be, it is common knowledge that excessive exposure to UV can in-fact increase the chance of skin cancer .
To minimize the possibility of adverse effects, some have suggested the use of other topical treatments in a rotation/combination approach [116, 117]. And perhaps as-long as a controlled therapy regimen is established, these risks can be eliminated altogether.
Simple sun exposure
Regular exposure to natural sunlight is known to improve psoriasis in the large majority of affected individuals, but these benefits can vary based on your geographic location [118, 119].
The method in which light therapy is believed to benefit psoriasis symptoms relates to the damaging effects of UV rays on skin cells and it’s immunosuppressive properties . Taken together, these factors can help offset both the hyper-proliferation of keratinocytes and stabilize the accompanying inflammatory T cell response.
Numerous systemic medication can be effective in the majority of cases. These medications include system immune system suppressive drugs, synthetic retinoids and fumaric acid esters .
The majority of systemic medications (excluding fumaric acid esters) used for psoriasis treatment are known to have cumulative organ toxicities and carry the biggest possibility for adverse effects [2, 122]. Thus, many researchers hold the opinion that they should be considered only after other approaches have been unsuccessful.
With surging demand for natural approaches to treatment, various plants have also been considered. But since the funding towards the research and testing of herbal medication is usually limited, the evidence for many of these approaches remains sparse.
Some noteworthy candidates include:
Topical application of a cream containing capsaicin (principal constituent of cayenne pepper) has been shown to offer significant relief of moderate to severe psoriasis in two isolated studies [123, 124].
- Aloe Vera
A Pakistani study of 60 patients showed a cream containing 0.5% aloe vera extract can be helpful in cases of moderate plaque psoriasis, with plaque healing rates as high as 82.8% . However, another more recent study of 40 participants contradicted these results .
- Milk Thistle
Anecdotal reports suggest milk thistle may relieve psoriasis by improving liver function . Although clinical studies for it’s effect on psoriasis do not exist, silymarin extracts are approved in Germany for the treatment of liver disease . And even in the absence of a direct effect on skin symptoms, the beneficial effect on liver function can be useful for offsetting many of the known metabolic abnormalities seen in psoriasis.
Curcumin (a constituent of turmeric) has been proposed to exert a beneficial effect on psoriasis through it’s anti-inflammatory properties. Sadly, preliminary investigation showed it’s effectiveness was lacking , but one interesting finding that did stick out from this study was that in individuals who responded to curcumin the results were excellent.
Due to it’s chronic nature, dietary adjustments presents a big opportunity for long term reversal of the underlying pathology behind psoriasis. However, the lack of evidence for specific dietary approaches and the large variation of hard to control individual factors has made this treatment approach somewhat of an enigma.
Nonetheless, the following dietary approaches have been shown to benefit both psoriasis symptoms and many of the overlapping cardiovascular abnormalities :
- Intermittent fasting
- Low caloric intake
- Restriction of meat and animal fats
- High intake of foods rich in omega 3 fatty acids
The primary explanation for the improvements seen with these dietary adjustments has been attributed to the low intake of omega 6 fatty acids, leading to a general reduction in inflammation.
This section featured a detailed examination of psoriasis. Granted the underlying mechanism is not fully understood, this review should help differentiate the condition from seborrheic dermatitis and make more informed treatment choices.
Here are some of the key-takeaways from the review:
- Psoriasis is an inflammatory skin condition similar to seborrheic dermatitis and characterized by inflammation, skin plaques, itchiness and tendency to relapse; unlike seborrheic dermatitis, it can affect any area of the skin
- The condition is considered to be a genetically inherited auto-immune disease triggered by environmental factors and the primary symptoms are the result of an abnormally high rate of skin cell division
- Plaque psoriasis is the most common form, but other unique types of psoriasis exist; pin-pointing the specific type is essential to narrowing down treatment options
- The three most unique types of psoriasis are guttate psoriasis (tear drop shaped spots), pustular psoriasis (blisters with pus) and psoriatic arthritis (inflammation of the joints)
- Stress, skin injury, systemic infection, certain medication, intestinal issues, poor dietary choices and bad lifestyle habits have all been identified as potential risk factors and known to impact symptom severity
- The majority of treatment options aim to modulate immune function and/or reduce the rate of skin cell division
- Corticosteroids are some of the most effective and commonly prescribed treatment options, but long term usage comes with a high risk of adverse effects
- Vitamin D derivatives and phototherapy have been shown to be equally as effective and if properly administered, they do not come with as high of a risk as corticosteroids
- Possible natural approaches to treatment include creams containing capsaicin, coal tar preparations, natural sunlight exposure, and anti-inflammatory dietary regimens
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