Certain changes in the microbiome may create unfavorable conditions a lead to a variety of skin issues and greater susceptibilities to infection. This phenomenon has been termed dysbiosis. And basically means an unfavorable change in the diversity of present skin microbes.
This section briefly examines the various findings on this subject and may provide some clues as to what leads to certain skin conditions.
Hard to make any valuable conclusions
Due to the overall complexity of how the skin operates and impact of other factors (such as health, nutrition and immune system function) making any valuable conclusion and connections becomes rather difficult.
Dysbiosis in Seborrheic Dermatitis
The most commonly discussed fungi species in the pathogenesis of seborrheic dermatitis has been malassezia. The majority of medical literature indicates that this species of fungi is directly responsible for seborrheic dermatitis.
Accordingly, many of the treatment options directly target inhibiting the malassezia fungi. And the relative success of these treatment throughout medical reviews has been another predominant factor that further acknowledges this believe.
Malassezia fungi are extremely common
Malassezia (a fungi known to be involved in the pathogenesis of dandruff and seborrheic dermatitis) appears to be the most abundant fungi on both normal and problematic human skin .
However, more recent studies comparing the skin of healthy individuals and those affected by seborrheic dermatitis have shown some potentially conflicting findings:
- No significant difference was seen in the abundance of malassezia species and for affected individuals lesion sites actually showed lower malassezia rates 
- Though malassezia restricta and staphylococcus epidermidis (staphylococcus) rates were marginally higher, propionibacterium acnes were significantly lower 
- The relationship between bacterial population and dandruff was more pronounced then the relationship with fungi. More specifically, affected areas of skin had higher rates of staphylococcus and lower rates of propionibacterium bacteria 
Additionally confusion comes from the simple fact that the malassezia family of fungi is one of the most abundant fungi species and it is present on the skin of most adults . And while some individuals encounter issues due to it’s presence, most people do not exhibit any issues.
Nonetheless, malassezia furfur and malassezia globosa have been shown to be present in significantly higher rates at lesion areas in individuals affected be seborrheic dermatitis .
In the end, many conflicting views still exist and no single theory currently exists. Regardless, examining malassezia alone is unlikely to produce any significant progress in the future. Instead research focus must shift to viewing the skin as a complex ecosystem where each component needs to be viewed in relation to all the others.
Dysbiosis in Atopic Dermatitis
Many researches have tried to identify specific differences in the microbiomes of individuals with healthy skin and those who suffer from atopic dermatitis issues.
These researchers were able to identify certain microbial differences (such as pronounced colonization and infection by staphylococcus aureus and/or diminished diversity of the overall bacterial community), several other factors were also identified:
- A diminished expression and/or function of antimicrobial peptides
- Mutations in the filaggrin protein (an essential component of epidermal barrier function)
- Mutations in the receptors and signaling molecules responsible for sensing microbes such as TLR2, CD14, and CARD4.
And this combination of findings makes it extremely difficult to pin-point any one specific cause behind atopic dermatitis.
Nonetheless, it must be noted that in some cases, improvement of the overall diversity of the microbiome resulted in pronounced improvement of atopic dermatitis symptoms.
Dysbiosis in Psoriasis
Psoriasis appears to represent a different issue than either atopic dermatitis or seborrheic dermatitis. This is because, with psoriasis, there does not appear to be any direct relation to infection.
Instead, psoriasis appears to be caused by an other auto-immune issues (such as arthritis, coronary vascular disease, etc.). Even though potential differences in the composition of the microbiome of individuals affected by psoriasis have been described, no specific micro-organisms were identified (neither fungal nor bacterial). Thus, the much larger and much more diversified nature of innate immune-related issues is suspected to be the more significant part of the issue.
Tiny mites are also a normal resident of our skin
Parasites such as the Demodex mite (believed to be partially responsible for the pathogenesis of rosacea) reside in the pilosebaceous unit (hair follicles and sebaceous glands) of both normal and malfunctioning skin.
This section described the various issues that could occur in the skin’s microbiome and their link to various skin disease. The key points discussed include:
- The term dysbiosis describes unfavorable changes in the microbial community of our skin and this has been linked to various skin disease
- The most popular belief is that the malassezi fungi is the main culprit responsible for seborrheic dermatitis symptoms
- Recent studies suggest the ratio between propionibacterium acnes and staphylococcus epidermidis may play a critical role in seborrheic dermatitis progression
- Currently there is no clear consensus as to the causative microorganism behind seborrheic dermatitis and many conflicting views exist
- In the case of atopic dermatitis, pronounced colonization of staphylococcus aureus and a diminished overall microbiome diversity are two of the most prominent findings
- Similar to seborrheic dermatitis, researchers studying the microbiome in atopic dermatitis have failed to reach any meaningful conclusions
- Psoriasis is more directly linked to overall immune function and though some microbiome differences exist, no single cause has been identified