June 11, 2010
Dear Mayo Clinic:
Is it true that ultraviolet light is actually good for some skin conditions?
It is true: ultraviolet (UV) light — a culprit behind sunburns, wrinkles and skin cancer — does offer benefits for some skin conditions. In a medical setting, the same ultraviolet light that's emitted from the sun can be carefully used as therapy for certain hard-to-treat skin problems and other medical conditions.
The main forms of ultraviolet light that reaches us from the sun are called ultraviolet A (UVA) and ultraviolet B (UVB). These are the same wavelengths of light that are used for medical therapies.
Ultraviolet light causes changes in cell DNA leading to cell damage and possible cell mutations that can turn a normal skin cell into a cancerous one. UVB rays are those responsible for sunburn. UVA rays penetrate skin more deeply, and it's increasingly recognized that they also set the stage for skin cancer development. UVA is the predominant type of ultraviolet light that comes from tanning beds.
With ultraviolet light therapy, certain aspects of UV light are harnessed for good. Although it's not fully known why certain skin conditions may respond to ultraviolet light, slowing the overgrowth of skin cells and altering the immune system are two mechanisms that appear to be at work.
Various ultraviolet treatments of the skin are potential therapy options for conditions including:
Ultraviolet light therapy is usually given in a medical clinic, where health care providers administer UV light therapy with a variety of devices. Equipment that may be used includes larger, full-body units such as light beds or body-sized light cabinets. Smaller equipment may include light cabinets for the hands or feet; a hand-held light; combs that emit light from the tines for reaching the scalp; and lasers, which can focus a high-intensity beam of UV light on a small area.
Therapy sessions may last from a few seconds to an hour and may take place two to seven days a week. It may take dozens of sessions before an adequate response is achieved.
Consistency is one of the keys to success. If the condition responds well to UV therapy, less frequent maintenance sessions may be needed. Once the condition has improved, patients may be able to switch to a less-frequent maintenance schedule. For some, maintenance therapy may be performed using a home ultraviolet unit.
Benefits aside, long-term UV therapy still has its downsides. Ultraviolet light therapy can dry out your skin and cause mild irritation. In addition, long-term UV therapy presents an increased risk of skin cancer. As with any form of treatment, the potential benefits need to be weighed against the potential risks. Fortunately, skin cancers generally can be removed and successfully treated when they are detected early. For those receiving UV therapy, an annual examination for skin cancer by a dermatologist is recommended.
— Mark Denis P. Davis, M.D., Dermatology, Mayo Clinic, Rochester, Minn.