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Retinoid is a derivative of vitamin A and can be used both orally and by direct application to the skin. It should not be confused with the vitamin A products bought from chemists or supermarkets as vitamin supplements.

Oral acitretin is an effective vitamin A-based treatment for psoriasis. It is only prescribed by dermatologists in a hospital setting for severe, extensive, refractory psoriasis. It has a long half-life, which means it remains in the body for a considerable period of time after treatment and it is persistent in tissues. In women this requires contraceptive measures during the course and for at least three years following therapy, as it can harm the development of unborn children.

The topical retinoid is used to treat mild to moderate plaque psoriasis by reducing the formation of patches of raised skin, helpful in palmar plantar as it reduces the thickening of the skin that can make dexterity difficult for everyday activities.

It also reduces the formation of cytokines and interleukins (two chemicals in the body that are responsible for causing inflammation). In other words, it acts by reducing the inflammation and by reducing the rate at which the skin cells develop plaques. However, if it comes in contact with normal skin it can cause irritation.

Topical retinoid specificity and its low systemic absorption mean that it produces fewer side effects than the earlier retinoid. It has a half-life of only 18 hours and does not accumulate on repeated administration.

Contraceptive measures are only necessary for women during treatment with topical agents. If taken orally, there is a three-year wash-out period, so retinoid is not commonly used in women of childbearing age.