Most affected are immunocompromised individuals. For example, rates as high as 53% have been noted in HIV-1 infected patients .
While males seem to be more prone than females, age related factors appear to have greater significance. And ethnicity doesn’t appear to have any significant influence .
Most commonly, seborrheic dermatitis is observed in:
- Infants within the first 3 to 4 months of life (infantile seborrheic dermatitis)
- Adolescents (around puberty)
- Individuals over 50 years old 
Regardless of age, seborrheic dermatitis has finally been gaining recognition as a condition which has a substantial negative effect on an individual’s quality of life .
How to Tell if You Have Seborrheic Dermatitis
So how do you know you have seborrheic dermatitis and not something else? Well, the easiest way to tell is if you have a combination of the following symptoms:
- Patches of greasy skin covered with skin flakes
- Patches of white or yellow scales
- Redness and irritation
- Itching, burning and crawling sensation of the skin
When the above symptoms occur on the scalp, the condition is most commonly referred to as dandruff. On the face, however, it almost always goes by the name of seborrheic dermatitis.
When the seborrheic dermatitis occurs elsewhere than the scalp, it also looks visually similar to eczema. These two conditions are quite similar in nature. The biggest difference appears to be the greasiness and scaling that accompanies seborrheic dermatitis. Eczema typically has dryer crusting and less flaking.
Is Seborrheic Dermatitis the Same as Dandruff?
Most researchers agree that dandruff is simply a less aggressive form of seborrheic dermatitis. And essentially, they are the same thing .
However, not all researchers agree. Some researches believe that the term dandruff should be used as a general term to describe any flaking that occurs on the scalp .
Others point to a specific difference in pathology. Specifically the fact that dandruff occurrence declines with age, while seborrheic dermatitis is very common amongst the elderly .
Areas Most Commonly Affected by Seborrheic Dermatitis
Most common seborrheic dermatitis affected areas (above the neck) are the scalp, hairline, eyebrows, nasal folds, melolabial folds, ears, chin and other hair-bearing areas of the face. Other common areas (below the neck) include the central chest, and genital region.
Treating seborrheic dermatitis on the scalp (dandruff) is the most straight-forward. Widely available dandruff shampoos can quickly produce good results.
Facial seborrheic dermatitis is more difficult to treat. Likely due it’s more aggressive behavior and the sensitive nature of the facial skin.
Why Does It Occur In These Areas?
For the most part, researches believe that this is due to these areas having the most sebaceous activity (sweat and oil production) .
Some believe it is not as straightforward as that. One study used thermal imagery to examine other possible factors affecting the location of seborrheic dermatitis. The study concluded that seborrheic dermatitis most commonly affected the warmer areas of the facial skin .
May the Increased Temperature Attract More Bacteria?
Perhaps the heightened facial temperature is responsible for attracting a greater amount of the bacteria. As more bacteria accumulate in these warmer patches of skin, the seborrheic dermatitis is triggered.
Though this single study provides an glimpse at the possible role skin temperature may play, it is my no means conclusive. The study is rather small and was not even performed on seborrheic dermatitis affected individuals.
Nonetheless, seeing the thermal images of the face, you can’t help but notice the distinct butterfly pattern seborrheic dermatitis typically exhibits.
This section went over some of the most important fundamentals of seborrheic dermatitis. Here is a quick recap:
- Seborrheic dermatitis affects about 1% to 5% of the healthy adult population, while dandruff rates may be closer to 40%.
- Immunocompromised individuals are most at risk, with rates as high as 53% reported for HIV-1 patients.
- Gender and ethnicity have little effect determining susceptibility, but age can have a significant impact.
- Seborrheic dermatitis is most common in infancy, adolescence and after the age of 50.
- Primary signs include skin flakes, itching, reddening, tightness, and general irritation.
- Most researchers agree that dandruff is a mild form of seborrheic dermatitis, however, some uncertainty exists.
- The scalp, hairline, eyebrows, nasal folds, melolabial folds, ears, chin, central chest and genital area are most commonly affected.
- Sebaceous gland activity is the leading explanation of why specific areas are typically affected, but temperature may also play a role.