Phototherapy, also called light therapy, is a treatment for psoriasis that uses controlled ultraviolet light to slow the overactive growth of skin cells and reduce inflammation. The most common form is narrowband UVB therapy, which is often used for widespread plaque psoriasis or psoriasis that has not responded well to creams alone. Treatments are usually done in a medical office or with a prescribed home light unit several times per week over a number of weeks. Phototherapy can help reduce redness, scaling, thickness, and itching without using systemic medications. It may be a good option when psoriasis covers larger areas of the body or when someone wants to avoid or delay pills or biologic injections. Possible downsides include time commitment, sunburn-like irritation, tanning, aging of the skin, and a potential increased risk of skin cancer with long-term or excessive ultraviolet exposure.