Patients usually need different topical treatments for three areas of the body

• The trunk and limbs
• The face and flexures (where the skin is thinner)
• The scalp.

The NICE guideline recommends that treatments be tried in a logical sequence until satisfactory products or regimens are found. People with psoriasis should be encouraged to keep a supply of their topical treatment at home so that treatment of a flare-up can be started without delay. 

• Emollients

Emollients restore pliability to the skin and reduce itching and shedding of skin scales. They can also help to prevent painful cracking and bleeding. Emollients that contain humectants, such as urea or glycerine, are more effective moisturisers and have longer-lasting effects. 

• Corticosteroids 

Topical corticosteroids are often effective for bringing a flare-up under control. If used incorrectly there are risks of local side effects such as skin atrophy (thinning or depression of skin), striae (stretch marks), telangiectasias (also known as spider veins) and the risk of rebound and worsening of psoriasis after discontinuation. 

In order to minimise these risks, potent corticosteroids should not be used continuously at any site for longer than eight weeks and very potent corticosteroids for no longer than four weeks. There should be a four-week break between courses of treatment with potent or very potent corticosteroids. Vitamin D, vitamin D analogues or coal tar products may be used during this time to control psoriasis.

• Vitamin D 

Vitamin D and vitamin D analogues inhibit proliferation and promote differentiation of keratinocytes, thereby ‘normalising’ skin cell behaviour in psoriatic plaques. They do not cause skin atrophy. Skin irritation resulting in transient increased redness, dryness and stinging or burning can be a problem so, for this reason, calcipotriol should not be used on the face or flexures. Calcitriol is less irritant and may be used on the face and sensitive flexural areas. 

It is important to ensure that adequate quantities are used – 0.5g (a fingertip unit) of calcipotriol ointment per 100cm2 of skin (approximately the area of a medium-sized adult palm.) The maximum weekly doses of the vitamin D analogues are limited to avoid the risk of hypercalcaemia (calcipotriol 100g, calcitriol 210g and tacalcitol 70g).

• Coal tar and dithranol 

Coal tar and dithranol preparations were used frequently in the past and are still included in the NICE guideline as options when other treatments have failed. Coal tar is present in a number of OTC products.