Allergic reactions often cause rashes. The rash may vary in size and severity, depending on its cause. Poison ivy, fragrances, and medications are some common substances that can cause an allergic rash.
A person can treat most allergic reaction rashes at home with over-the-counter (OTC) medications. However, if someone is having difficulty breathing during an allergic reaction, they require medical attention.
In this article, we examine the different causes of rashes from allergic reactions, how to treat and prevent them, and when to see a doctor.
An allergic reaction occurs when a person’s immune system becomes overly sensitive to a typically harmless substance, or allergen.
The World Allergy Organization (WAO) estimate that globally between 10–40% of all individuals experience some type of allergic reaction.
Allergens can enter the body in several ways. These include:
- through contact with the skin
- by mouth, through swallowing or eating
- through an injection
- when inhaled
Once an allergen enters the body, it can trigger an inflammatory response, which may include a rash on the skin.
Contact dermatitis occurs when a person touches something they are allergic to. Typically, a person needs to come into contact with the allergen repeated times before a reaction occurs. The rash can appear anywhere from 24–48 hours later.
Almost any substance in the environment can trigger an allergic reaction with a rash. We list some of the most common below.
Within a few days of contact with one of these plants, a person may develop a bumpy, itchy red rash. The rash typically forms a line on the arms, legs, or areas where the plant oil has touched the skin.
The rash may continue to develop over several days and form small fluid-filled blisters. People may spread the rash by touching non-affected areas after affected ones.
Several chemicals can cause an allergic reaction when they come into contact with a person’s skin. These include:
A chemical rash often resembles a burn. It may present with swelling or blistering, or have oval-shaped flaky or dry patches.
The allergic reaction is usually limited to the area of the skin that directly touched the allergen.
Any drug may cause an allergic reaction. The most According to a 2019 article, common medications that can cause an allergic rash include:
- antibiotics, such as penicillin and sulfa
- neomycin and bacitracin
- nonsteroidal anti-inflammatory drugs (NSAIDS)
- birth control pills
- intravenous (IV) contrast dyes or blood transfusions
During immediate reactions, the rash will usually consist of hives, which are raised red lesions on the skin.
A medication reaction often starts on the trunk and may spread to the arms, legs, palms, soles, and the mouth. This type of rash onset occurs soon after taking medicine.
Other delayed reactions and rashes can occur between days to weeks later. An allergic reaction can occur even after a person stops taking the medication. Topical antibiotics, such as neomycin and bacitracin, can also cause contact dermatitis.
Foods and food additives
A food allergy reaction is most often associated with hives or swelling. The foods that cause most allergic reactions include:
- tree nuts (walnuts, almonds, pine nuts, brazil nuts, pecans, cashews, pistachios)
- fish and shellfish
While rarer, a person may develop hives when they inhale an allergen. Examples of respiratory allergens include:
- mold spores
- dust mites
- animal dander
In addition to a rash, other symptoms that can occur with an allergic reaction may include:
- a burning sensation
- a low grade fever
- wheezing or shortness of breath
A healthcare professional can usually diagnose a rash caused by an allergic reaction by obtaining a person’s medical history and examining the rash.
Other tests that can help determine the cause of an allergic rash may include a punch biopsy or allergy skin tests.
The American Academy of Allergy, Asthma, and Immunology (AAAAI) say that once an allergic reaction starts, it may take 14–28 days to go away, even with treatment (depending on the type of reaction).
Treatment options include:
- corticosteroid creams
- nonsteroidal creams
- cool compresses
- oatmeal baths
- OTC anti-itch lotions such as calamine
- OTC antihistamines, such a Benadryl or Zyrtec
- prescription oral steroid medications, such as prednisone
- epinephrine injection
Babies have sensitive skin and may develop an allergic rash in response to soaps, animal dander, or nickel. Babies may also experience an allergic reaction to an antibiotic or new food.
An allergic rash may appear anywhere on a baby’s skin. The rash may appear as:
- clusters of tiny red bumps
- scaly, dry skin
- patches of red in skin folds
A person should see a doctor if their rash:
- starts suddenly and spreads quickly
- begins after starting a new medication
- has accompanying symptoms, such as severe itching, pain, or fever
- is developing large blisters or swelling
- is showing signs of infection, such as warmth and pus
- is all over the body
- persists despite treatment
In rare instances, an allergic reaction can result in anaphylaxis, or difficulty breathing due to rapid swelling of the airways. The AAFA state that medicines, food, and insect stings are the most common triggers for anaphylaxis.
Anaphylaxis is an emergency. A person needs emergency care if they experience:
- difficulty breathing or feeling like the throat is closing up
- swelling of the face, lips, or tongue
- confusion or loss of consciousness
- a drop in blood pressure
- blueish color to the skin
- vomiting or diarrhea
- abdominal cramps
A person who has a history of anaphylaxis should always carry an EpiPen injector.
Most people can manage rashes due to an allergic reaction at home, and, according to the National Institutes for Health (NIH), they usually disappear after a few days or weeks.
If someone can identify the specific cause of an allergic reaction, the outlook is excellent, as they can avoid the trigger.
To prevent an allergic rash, a person should avoid coming into contact with known or common allergic triggers by:
- using unscented, non-fragrance laundry soap and body products
- wearing gloves when there is a chance of exposure to chemicals or plant oils
- washing after possible contact with an allergen
- wearing a medical alert bracelet that identifies a drug allergy
Allergic reactions are a common medical problem. Typical triggers for allergic rashes include:
- animal dander
- poisonous plants
Most allergic reaction rashes are not life threatening, and a person can usually treat the rash at home with OTC medications.
Rashes that continue to spread or are accompanied by fever or breathing issues need medical attention.
With careful avoidance of common triggers, a person can successfully manage and prevent rashes caused by allergic reactions.