Allergies, which are caused by an overactive immune system, can result in a number of different symptoms. Some kinds of allergies can cause a rash. Often the rash is not a serious medical problem, but such rashes can cause significant discomfort. Patients suffering from rashes due to allergy should avoid the substance that triggers the rash and may benefit from a variety of treatments.
Mechanism
Allergies are caused by substances, known as allergens, that activate the immune system. Normally the immune system ignores these molecules, but patients with allergies have special proteins, called IgE antibodies, which recognize these allergens, the American Academy of Allergy and Asthma and Immunology explains. When these antibodies bind to their allergens, they send out chemical signals that activate other immune cells. This leads to swelling and inflammation that can cause a rash in patient's with these kind of allergies. IgE antibodies are designed to bind to only one molecule, so patients with allergies to one substance may not have allergies to anything else.
Types of Allergic Rashes
There are a few different kinds of allergies which can cause a rash or hives, the Mayo Clinic explains. Atopic dermatitis, which is also known as eczema, is an allergic reaction to substances that come into contact with the skin. Patients with atopic dermatitis may suffer from patches of itchy, flaky, red skin. Food and drug allergies can also cause a rash or hives to develop; in this case, the allergic reaction occurs throughout the body and can cause a variety of other symptoms aside from the dermatological problems.
Anaphylaxis
One danger of food and drug allergies is a condition known as anaphylaxis, which is a very severe kind of allergic reaction. In addition to a rash, anaphylaxis can also cause the patient to become light-headed, lose consciousness and develop a very rapid and weak pulse. Patients may also have extreme trouble breathing due to swelling of the airways, and may also experience nausea and vomiting. Anaphylaxis is a medical emergency and typically is treated with an epinephrine injection.
Diagnosis
With rashes that are caused by allergies, the allergen can sometimes be identified by taking a look at the locations of the rash and talking with the patient about what activities he was doing before the rash appeared, the American Academy of Dermatology notes. In some cases, this is not enough to determine the cause of the rash and more intensive tests may be needed. One test, called a patch or prick test, involves placing small amounts of potential allergens on or under the patient's skin to determine if they can cause swelling and redness. This allows for the testing of multiple different allergens in a short period of time.
Treatment
Mild allergic reactions, the American Academy of Dermatology explains, can be treated with corticosteroid creams or antihistamines, as both treatments will help block the chemical signals involved in the allergic reaction. Patients may also need to apply a moist compress to blistered areas to help them heal. More severe cases may require oral corticosteroids, antibiotics, and medications that suppress the immune system. In all cases, patients should attempt to avoid the allergen whenever possible and instead try to use substitute products which do not contain allergens.
