Phototherapy (light therapy) : Ultraviolet (UVL) light, a portion of the solar spectrum with wavelengths between 290-400 nm, can have beneficial effects on psoriatic skin presumably by altering certain immune functions. Disease that is considered too extensive to be treated by topical approaches, that is usually greater than 5%-10% of the total body surface area, is an appropriate indication for this sort of treatment. Resistance to conventional topical treatment is another indication for light therapy. Although normal sunlight contains these wavelengths, self-exposure to sunlight must be done in under controlled conditions to minimize burns. In a physician's office, control of the amount of light energy administered to each patient is essential. Medical light sources use special wavelengths of light and timers to assure the correct dosage of light. Sunlamps and tanning booths are not acceptable substitutes for medical light sources. Ultraviolet light from any source is known to produce skin cancer , but this side effect is minimized when the light is appropriately administered in a physician's office.
Transdermal patches can be a very precise time released method of delivering a drug. Cutting a patch in half might affect the dose delivered. The release of the active component from a transdermal delivery system (patch) may be controlled by diffusion through the adhesive which covers the whole patch, by diffusion through a membrane which may only have adhesive on the patch rim or drug release may be controlled by release from a polymer matrix. Cutting a patch might cause rapid dehydration of the base of the medicine and affect the rate of diffusion.