How long does an allergic rash last?

"060521peanuts" is Copyrighted by Flickr user: Dan4th (Dan4th Nicholas) under the Creative Commons Attribution license.

If you suddenly become itchy and begin to break out in hives anywhere on your body, you may be experiencing an allergic rash. For most people, an allergic rash is best avoided by steering clear of what triggers it.

For others, the cause of their allergic rash may never be discovered, either because it is only experienced once or because the exact trigger cannot be identified.

What is an Allergic Rash?

An allergic rash is denoted by swollen, itchy skin that may also become cracked and painful. Red, itchy hives may also present themselves during an allergic skin reaction and can be quite uncomfortable. The itching that is involved with an allergic rash usually becomes worse the more it is scratched. Allergic rashes usually have triggers that become recognisable after the first few outbreaks. Most allergic rashes will last approximately 1 to 14 days and may resolve on their own or with treatment.


Sometimes allergic rashes can be caused by autoimmune disorders such as lupus and scleroderma. Aetna IntelliHealth explains that the allergic rashes associated with autoimmune disorders are a result of an overactive immune system that mistakenly attacks the skin. Allergic reactions that are autoimmune related are referred to as "flare-ups." The flare-ups can last days or weeks and are completely dependent on disease progression.


Allergic rashes that are caused by plants are often referred to as "contact dermatitis" and are a familiar sight to people who are allergic to poisonous plants such as poison ivy and poison sumac. Medicine reports that the allergic rash associated with plants can last as long as two to three weeks before clearing up.

Viruses, Bacteria and Fungus

Allergic skin rashes can also develop as a result of fungal infections as well as, infections caused by bacteria and fungus. Viral infections such as herpes and bacterial infections associated with chickenpox are notorious for causing allergic skin reactions. Fungal infections like that of ringworm can also cause the skin to swell and become irritated by an allergic skin rash. explains that allergic rashes that develop as a result of viruses, bacteria or fungus, can last anywhere between one and 14 days.

Irritants, Foods and Common Allergies

Allergic rashes can also be caused by common allergies and environmental irritants. For instance, pollen and dust mites are common household allergies that can cause an allergic skin rash. Environmental irritants such as chemicals can cause an allergic skin rash. Food allergies, such as those associated with peanut butter, also can cause an allergic response that affects the skin. According to MD, allergic skin rashes caused by irritants, food or common allergies are often treated with steroids and may last several days.


A medications such as an antibiotic may generate an allergic reaction that causes a skin rash. When this happens the attending physician may need to substitute a different kind of drug. Merck reports that allergic skin rashes associated with medications can be quite itchy and uncomfortable and can potentially harm the organs inside the body. For this reason, it is important that any allergic reaction concerning medications be documented in the patient's health file. An allergic skin rash that is caused by medication may last for weeks before the source is identified and usually resolves once the medication is stopped.