Psoriasis is a relatively common condition that affects approximately 2-3% of people in the United States according to the National Psoriasis Foundation1, and that equates to a staggering number of almost 8 million Americans. One of the most common sites of involvement is the scalp, and for that reason, it may be easily confused with seborrheic dermatitis (SD). These two conditions are often viewed by dermatologists as being on a diagnostic continuum, with a more mild case being viewed as SD, and a more severe case being diagnosed as psoriasis. Nevertheless, the reasons why the conditions exist and have disparate features is important to understand.
As reviewed in the October 2019 LivSo blog post, SD often results in dry, itchy, flaky patches on the scalp and is associated with dandruff, but may also affect other body sites like the face (eyebrow regions, sides of the nose), and chest. Psoriasis also commonly affects the scalp, but typically also is found on the extensor surfaces of the arms (elbows), legs (knees), and lower back. The rashes, known as plaques, may be fairly small in size like a coin, or larger covering an area the size of a note card, or more. The plaques are usually scaly with a white or silvery sheen depending on the age of the lesion, and other factors like skin color. SD may affect infants, teens, and adults alike, and the common form is not typically correlated with any internal disease. Psoriasis usually begins in early adulthood, between age 15-25, and may also be associated with arthritis, which may develop later, between 30-50 years of age.
Seborrheic dermatitis is typically thought to be correlated with yeast levels (malassezia, sp.) and the inflammatory response to those organisms. On the other hand, psoriasis is thought to be caused by a dysregulation in the inflammatory systems that regulate our skin’s structure and function. With psoriasis, rapid cell production occurs - sometimes up to seven times faster than normal. The skin cannot shed these cells fast enough, so the skin’s top layer (stratum corneum) thickens and there are changes to the underlying layers of the skin - the epidermis and dermis, along with modifications of the blood vessels. These conditions, especially psoriasis, may be associated with other health issues beyond the expected skin discomfort.
It has been demonstrated that people with psoriasis have increased levels of inflammation internally which is associated with higher rates of cardiovascular disease. Mental health is also a concern in these patients because depression is found in higher rates among those with psoriasis, along with gastrointestinal, kidney, and metabolic disorders, and even some cancers2. For all of the above reasons, a correct diagnosis is of the utmost importance.
The symptoms associated with psoriasis and SD are not always easy to distinguish from one another and often requires the help of a dermatologist. A dermatologist can listen to the patient’s history, examine the skin including the scalp and nails (often revealing clues like nail pitting which may occur in psoriasis), and even do a skin biopsy if necessary. All of these steps are critical to establishing a proper diagnosis so that the most effective treatments can be initiated. In the case of psoriasis, proper treatment may prevent uncomfortable rashes and halt joint damage that can be irreversible.
Both psoriasis and SD can be treated with topical solutions including, antifungal shampoos, lotions, creams, ointments, and anti-inflammatory products and compounds that help remove scale and flaking while soothing the skin. However, more difficult cases of psoriasis, particularly with extensive skin involvement or joint pain require internal medications like methotrexate, apremilast, or one of the many biologic drugs that specifically target the signals in the body responsible for driving psoriasis (TNF, IL-17, IL-23, and others). Despite these efforts, people with psoriasis still need to have personal care products for routine grooming suited for their needs just like anyone else. When the condition is present on the scalp, it is important to cleanse and moisturize the hair while relieving dryness, flaking and itching. For this reason, people suffering from psoriasis may find products that are used to help with SD may also be helpful with psoriasis and vice-versa.
In summary, if you or someone close to you has a condition that seems like dandruff, but does not respond to typical treatments for seborrheic dermatitis or dry scalp, please see a dermatologist! It may represent something that is truly more than skin deep.
Live free & clear,
Shari Hicks-Graham, MD
REFERENCES
1. psoriasis.org/about-psoriasis/causes
2. Takeshita, et al. Psoriasis and comorbid diseases: Epidemiology. J Am Acad Dermatol 2017;76:377-90.