May 27, 2011
Dear Mayo Clinic:
Is psoriasis related to allergies?
What causes psoriasis — a common skin condition — is unclear, but no evidence associates psoriasis with allergies. Instead, the condition appears to result from a different type of immune system response within the body.
In people who have psoriasis, skin cells build up rapidly on the surface of the skin. Normally, skin grows and sheds in 28-day cycles. But for skin affected by psoriasis, that cycle shrinks to just three days. This rapid cycle causes inflammation and overgrowth, and produces patches of red, scaly skin that may become dry and cracked.
Psoriasis can be a painful and cosmetically disturbing disease. Often, the scalp, hands, feet, fingernails and toenails — visible areas on the body — are affected. Psoriasis can also occur inside the mouth, making eating and speaking difficult at times. In some people, the disease can affect joints, resulting in joint swelling, stiffness and pain.
Psoriasis can erupt without warning. When it first appears, many people, understandably, want a quick cure. They may hope that the psoriasis was caused by something in the environment or by something they ate. With that information, they reason, they can avoid the same stimulus in the future. However, research has found no links between any type of allergy-producing substance (allergen) and psoriasis.
Allergies occur when the immune system reacts to a foreign substance, such as pollen or pet dander, by producing antibodies. Usually antibodies protect the body from unwanted invaders that could cause illness or infection. With allergies, the immune system makes antibodies to destroy the allergen because it incorrectly detects something as harmful. The ensuing reaction to an allergen can inflame the skin, sinuses, airways or digestive system.
Although psoriasis appears to be an immune system response, it is not an allergic reaction. The immune system isn't attempting to destroy something. Rather, it's prompting an overgrowth of healthy skin cells. That's why allergy treatments are not effective for psoriasis.
A variety of factors can increase the risk of developing psoriasis, including smoking and obesity. Having another inflammatory medical condition, such as multiple sclerosis, heart disease or inflammatory bowel disease, also can increase risk. In some cases, psoriasis can be hereditary.
Psoriasis is a long-term chronic condition, currently without a cure. But treatments are available that can either remove and smooth the patches of scaly skin or disrupt the rapid skin growth cycle. First, there are creams and ointments that can be applied to the skin, such as salicylic acid, tar treatments, topical vitamin D and topical steroids. If psoriasis is mild to moderate, these topical treatments may suffice.
Second, light therapy has been shown to reduce the inflammation and scaling of psoriasis. Moderate amounts of sunlight can be helpful, as can controlled doses of ultraviolet light, if recommended by your doctor. Tanning beds should not be used as a source of light therapy, because they increase the risk of skin cancer and also can burn the skin. When skin affected by psoriasis burns, the psoriasis can spread very rapidly.
Third, for severe cases that don't respond to other treatments, or if psoriasis affects the joints, some oral or injectable medicines may be used to help reduce the production of skin cells and decrease joint symptoms.
As a chronic condition, psoriasis often comes and goes, and treatments that work once may not work when repeated. If you have psoriasis, find a dermatologist who can monitor your condition over time and help you manage the disease to minimize its effect on your daily activities and quality of life.
— Dawn Davis, M.D., Dermatology, Mayo Clinic, Rochester, Minn.