Some causes of an unexplained rash are an allergic reaction, abrasive clothing, and chronic fatigue syndrome. An allergic reaction is an especially common cause of unexplained rashes, but the patient often never finds out what he or she came into contact with that triggered the reaction. Chronic fatigue syndrome is a rarer cause, but researchers are unsure how rare due to how poorly understood the condition is and how many people go undiagnosed worldwide. In a few cases, the rash is caused by an immune response because of an autoimmune disorder.
Often a mystery rash is caused by an allergic reaction to a foreign or unusual substance. Sometimes allergic reactions are minor and result only in symptoms such as rashes and itchiness, but other times can be more dangerous. One thing that often causes an unusual allergic reaction is a new laundry detergent, so it is usually a good idea to consider new substances that have been introduced into an environment when attempting to root out the cause of an allergic reaction. Bug bites, foods, and other substances can also result in an allergic reaction and unexplained rash.
Sometimes a rash is caused by something as simple as abrasive clothing or friction. New clothing is more suspect than old clothing when people find themselves with an unexplained rash, possibly due to abrasive material. Other times the rash is caused by friction, either friction against a person’s own skin, clothing, or something else that chafes the skin and eventually causes it to break out in a rash.
Chronic fatigue syndrome is a condition wherein the patient has unexplained fatigue for at least six months. There is no way of diagnosing a patient with chronic fatigue other than ruling out all other potential causes of the fatigue and considering any other symptoms. Some people with chronic fatigue syndrome develop a mystery rash, while others suffer from headaches and low-grade afternoon fever. As causes of unexplained rashes go, this is believed to be a rather uncommon one, but the vast majority of people with chronic fatigue syndrome go undiagnosed.
Autoimmune progesterone dermatitis (APD) is a condition that causes women to develop rashes because of their menstrual cycle. This health problem is rare and not fully understood, but researchers believe the skin rash is a response to the hormonal changes in the woman’s body. Women with APD develop a rash before their period, which goes away within a few days of actually menstruating. Those who undergo hormone therapy, such as taking contraceptive pills, may be more likely to experience APD.