This disease may occur in isolation or with any other form of psoriasis. At least half of all the people who have psoriasis have it on their scalp. Other skin disorders, such as seborrheic dermatitis, may look similar to psoriasis. However, scalp psoriasis appears powdery with a silvery sheen, while seborrheic dermatitis appears yellowish and greasy. The back of the head is a common site but multiple discrete areas of the scalp or the whole scalp may be affected. Scalp psoriasis is characterised by thick silvery white scale on patches of very red skin. It may extend slightly beyond the hairline. Scalp psoriasis, even though often adequately camouflaged by the hair, is often a source of social embarrassment due to flaking of the scale and severe 'dandruff'. Scalp psoriasis may not cause any symptoms at all or may be extremely itchy. It tends to be a chronic problem, lasting many years.
In very severe cases there may be some temporary mild localised hair loss but scalp psoriasis does not cause permanent balding.
Sebopsoriasis is an overlap between psoriasis and another common skin condition, seborrhoeic dermatitis. There tends to be less silvery scale than psoriasis and more yellowish, greasy scale. It also tends to localise to the scalp, face and anterior chest in a similar pattern to that seen in seborrhoeic dermatitis. Sebo-psoriasis has a deeper red colour, more defined margins and a thicker scale than typically seen in seborrhoeic dermatitis alone.
Pityriasis amiantacea is a condition of the scalp characterised by thick, yellow-white scales densely coating the scalp skin and adhering to the scalp hairs as they exit the scalp. They are arranged in an overlapping manner like tiles on a roof or flakes of asbestos, hence the name. The underlying scalp skin may appear normal, aside from the scale, or may be reddened or scaly. Pityriasis amiantacea is often present without any obvious underlying cause, but may be associated with psoriasis, lichen simplex or seborrhoeic dermatitis.
Pityriasis amiantacea usually affects only part of the scalp but may occasionally involve the whole scalp. Young girls may have localised pityriasis amiantacea extending into the scalp from areas of chronic fissures in the skin behind the ears. It may extend from an area of lichen simplex of the scalp.
Some hair loss is common is areas of pityriasis amiantacea but hair regrows normally if the condition is effectively treated. This hair loss is sometimes aggravated by the difficulty in combing the hair due to the very adherent, thick scale at the base of the hair shafts. If additional complications such as infection occur then hair loss may be associated with scarring and be permanent.
The term "tinea amiantacea" is incorrect, because fungal infection, tinea capitis, is a very rare reason for this type of scaling.
Psoriasis is an autoimmune condition involving the T lymphocyte, a type of white blood cell. Normally, the time to manufacture and shed skin cells is about 28 days. In psoriasis, the process is approximately 7 times faster and the outer cells are poorly formed and don’t shed properly, they tend to pile up on the skin that produces scale.
Just like other types of psoriasis, scalp psoriasis begins in the immune system, mainly with a type of white blood cell called a T cell. T cells help protect the body against infection and disease. With psoriasis, T cells are put into action by mistake. They become so active that they set off other immune responses. This leads to swelling and fast turnover of skin cells.
People with scalp psoriasis may notice that sometimes the skin gets better and sometimes it gets worse. Things that can cause scalp psoriasis to get worse include:
- Changes in weather that dry the skin
- Certain medicines.
- When scalp psoriasis develops, people have one or more of these signs and symptoms:
- Reddish plaque on the scalp. Plaques range from barely noticeable to thick and inflamed.
- Silvery-white scale. This often develops on the scalp and can be mistaken for dandruff.
- Dandruff-like flaking. This is common due to the continual shedding of the new skin cells. Unlike dandruff, scalp psoriasis causes a silvery sheen and dry scale on the scalp.
- Dry scalp. The scalp may be so dry that the skin cracks and bleeds.
- Itching. This is one of the most common symptoms. For some the itch is mild; others have intense itching that can interfere with everyday life and cause them to lose sleep.
- Bleeding. Because scalp psoriasis can be very itchy, almost everyone scratches. This can cause the scalp to bleed. Scratching also injures the skin, which tends to worsen the psoriasis. This is why dermatologists tell their patients “Try not to scratch your scalp.”
- Burning sensation or soreness. The scalp can burn. It can feel extremely sore.
- Temporary hair loss. Scratching the scalp a lot or forcefully removing scale can cause hair loss. Once the scalp psoriasis clears, hair usually re-grows.
These signs and symptoms can come and go. Some people have only one mild flare. Others experience flare-ups that range in intensity, with some flare-ups being milder than other flare-ups. Many things can trigger a flare-up, including stress, cold, and a dry environment.
Scalp psoriasis requires slightly different regimes from psoriasis affecting the skin elsewhere. This is due to hair, which makes application of many topical products difficult and protects the scalp from the effects of ultraviolet light. Unfortunately, many scalp treatments for scalp psoriasis are messy and smelly. Most treatments will need to be used regularly for several weeks before a benefit is seen.
Special medicated shampoos can be purchased from the chemist.
Coal tar shampoos are suitable for most patients with scalp psoriasis.
Ketoconazole, ciclopirox, zinc pyrithione and other antifungal shampoos are effective for dandruff and seborrhoeic dermatitis. They have varying effect in sebopsoriasis and psoriasis.
The shampoos work best if rubbed into the scalp well, and left in for 5 or 10 minutes and then reapplied. They are safe for daily use but may irritate if applied more than twice weekly. If you dislike the smell of coal tar, try shampooing again with a favourite brand, and use a conditioner.
More severe cases require leave-on scalp applications.
Alcohol-based, foam or lotion forms of topical steroid and calcipotriol can reduce redness and itch but they don't lift scale very well. Use topical steroids intermittently; overuse results in more extensive and severe psoriasis.
Salicylic acid and coal tar creams work much better, but are messy. Coconut oil compound ointment is a combination of coal tar, salicylic acid and sulphur and seems particularly effective. Leave on for at least an hour and shampoo off later. Most people rub the cream into the plaques at night and wash it off in the morning.
Dithranol may be effective but is difficult to use and may be messy as it stains hair and fabrics.
Use the scalp preparation daily at first then as the condition improves, reduce the frequency. Unfortunately in many cases the scale soon builds up again, so the creams may have to be applied regularly to keep the scalp clear.
Cutting hair short helps control scalp psoriasis, probably by making the treatments easier to apply, but is not appealing to everyone.
Phototherapy is effective for chronic plaque psoriasis but difficult to deliver to the scalp. Special targeted devices and UVB combs have been devised, and appear very helpful. In some cases prolonged clearance has resulted from a course of treatment.
Systemic agents may be justified for a few patients with severe scalp psoriasis that has failed to respond to treatments described above. These include acitretin, methotrexate, ciclosporin and bioloigcal response mediators.