How do psoriasis and seborrheic dermatitis differ?
Both of these skin conditions may affect the scalp, which is why they are often confused.
One of the major differences between seborrheic dermatitis and scalp psoriasis is their appearance. Scalp psoriasis appears powdery and has a silver sheen, whereas seborrheic dermatitis is more likely to appear yellow and greasy.
Other differences in the conditions can be understood by exploring the symptoms, causes and treatments for each.
Differences in symptoms
Understanding the differences between seborrheic dermatitis and psoriasis can help people to seek appropriate help from a doctor. A swift diagnosis means the skin condition can be treated quickly and efficiently.
Seborrheic dermatitis symptoms
Seborrheic dermatitis can cause crusty white flakes or yellow scales, especially on the scalp and face.
Seborrheic dermatitis usually appears on the scalp, although it can sometimes be found on the face, upper chest, and back.
- crusty white flakes
- greasy yellow scales
- red and swollen skin
- skin that may itch or burn
While psoriasis can affect the scalp, it is more likely to affect other areas of the body too, such as the elbows or knees.
Psoriasis causes raised scaly patches to appear on the skin. These usually develop on the outside of the elbows, the knees, or the scalp.
Types of psoriasis
There are five main types of psoriasis:
- plaque psoriasis
- guttate psoriasis
- inverse psoriasis
- pustular psoriasis
- erythrodermic psoriasis
The most common type of psoriasis is plaque psoriasis.
This presents as raised, red patches with a silvery-white build-up of dead skin cells. These lesions can be itchy and painful.
Guttate is a type of psoriasis that looks like small, dotted lesions. About 10 percent of people with psoriasis have this version of the condition.
Inverse psoriasis appears as red, smooth, shiny lesions that can affect skin folds, such as the groin, armpits, and backs of the knees.
As inverse psoriasis affects the folds of the skin, these areas can become prone to yeast or fungal infections.
Pustular psoriasis usually affects the hands and feet, and is characterized by white blisters of pus surrounded by red skin.
The most rare and severe form of psoriasis is erythrodermic psoriasis. This appears as a "fiery" redness that spreads over most of the body and is very painful.
People with erythrodermic psoriasis may experience severe itching, and their skin may peel off in sheets. Only about 3 percent of people with psoriasis get erythrodermic psoriasis.
Causes of seborrheic dermatitis and psoriasis
Scientists do not know the exact cause of seborrheic dermatitis, but genes and hormones are known to play a role.
Things that can trigger seborrheic dermatitis include:
Seborrheic dermatitis is sometimes triggered by harsh soaps and detergents.
- hormone changes
- harsh detergents
- dry weather
- micro-organisms on the skin
Diseases that impact the immune system, such as HIV and AIDS, can make the symptoms of seborrheic dermatitis worse. Diseases that affect the nervous system, such as Parkinson's may also aggravate symptoms.
The exact causes of psoriasis are also uncertain, but scientists know that genes and the immune system influence the condition.
When people have psoriasis, the skin cells grow more quickly than they do in people without this condition, which causes lesions to build up. Guttate psoriasis can often be triggered by strep infection.
People can get seborrheic dermatitis at any age, and it is slightly more common in men than in women.
Men and women are equally as likely to get psoriasis, and it is slightly more common in white Americans than African-Americans.
People can develop psoriasis at any age, although it often occurs between the ages of 15 and 35. In very rare cases, infants may develop psoriasis.
There are a number of treatments available for both seborrheic dermatitis and psoriasis. Treatments differ for each condition and the effectiveness of each treatment can vary from person to person.
Seborrheic dermatitis treatment
Mild cases of seborrheic dermatitis can be treated with topical antifungal cream. Medicated shampoo can also help. Examples of these include:
- selenium sulfide
- coal tar
- zinc pyrithione
More severe cases may require treatment with corticosteroids to reduce inflammation.
Corticosteroids may not be appropriate if the person has been exposed to corticosteroids for a long period previously. If this is the case a doctor might prescribe another type of medication, called topical calcineurin inhibitors.
Examples of topical calcineurin inhibitors include:
- tacrolimus (Protopic)
- pimecrolimus (Elidel)
Oral antifungal medication may be used for people severely affected by seborrheic dermatitis.
Tar products and salicylic acid are known to be effective for treating mild scalp psoriasis.
There are many medicated shampoos that are available over the counter to treat scalp lesions and help reduce itching.
If the lesions are very mild and only affect a few areas, a doctor may give the person injections of steroids.
More severe cases of scalp psoriasis may require topical treatments, such as:
There are a variety of topical creams which may be prescribed to treat psoriasis on the scalp.
- anthralin (Dritho-Scalp)
- calcipotriene (Dovonex)
- calcipotriene and betamethasone dipropionate (Taclonex)
- tazarotene (Tazorac)
If these topical medications are not effective, then a doctor may recommend:
- methotrexate (Trexall)
- cyclosporine (Gengraf, Neoral, SandIMMUNE)
- acitretin (Soriatene)
People with more severe scalp psoriasis may need to try several treatments before they find the one that works for them.
After repeated use, a person's psoriasis may become less responsive to the medication. If this happens, they may need a combination of treatments, which they can use in rotation.
Tacrolimus or pimecrolimus may be effective at relieving symptoms of psoriasis on the face and can help to avoid the potential side effects of topical steroids.
Ultraviolet light may also be used as a treatment for psoriasis. However, it will only be used for genital psoriasis in special circumstances because overexposure to ultraviolet light can burn the skin of the genitals.
A product called "Castellani's Paint" (Castederm) may be prescribed for people with inverse psoriasis. This is a liquid that is painted onto the affected skin and helps to dry the moist lesions in the folds of the skin.
Moderate to severe psoriasis can be treated with biological medications such as:
- Cimzia (certolizumab pegol)
- Enbrel (etanercept)
- Humira (adalimumab)
- Remicade (infliximab)
- Simponi (golimumab)
When to see a doctor
A person should see their doctor if they are experiencing symptoms that could be either seborrheic dermatitis or psoriasis.
Seborrheic dermatitis and psoriasis cannot be identified using a test. So, a doctor will ask people questions about their medical history to determine what the underlying condition is.
The doctor may also remove a small sample of skin (a biopsy) in order to help make their diagnosis.