Treatments for psoriasis can generally be classified as “topical” or “systemic” based on how the medication reaches psoriatic skin.
Topical treatments include creams, lotions, ointments, solutions, or foam directly applied to skin affected by psoriasis.
Topical treatments are composed of an active ingredient mixed into a vehicle or base, usually a cream or ointment, to allow the active ingredient to enter the skin for treatment.
Some forms of light treatment, such as UVB and lasers, have mostly local effects and act more like a topical treatment; others, such as PUVA, appear to work both locally and systemically.
Topical treatments are best for small areas of psoriasis, for people who prefer not to take oral medications, and for people who have other illnesses that are being treated at the same time. For most people with psoriasis, topical treatments will control their psoriasis well, and they may never need systemic treatment.
Systemic treatment is given by mouth, by injection, or by intravenous infusion, and reaches the entire body. It is especially useful for patients with moderate or severe psoriasis, or for people with psoriatic arthritis.
People with psoriasis scattered all over the body in small spots may prefer systemic treatment because of the length of time needed to treat each small spot with topical treatments.
Those with more extensive involvement, associated arthritis, psoriasis that is particularly painful and itchy, or resistant to topical treatment may want to consider systemic treatment.
The main disadvantage to this approach is that the entire body is exposed to the medication and therefore affected by the effects and side effects.