Plus, what to do if they don't clear up after treatment.

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The list of things your body can have an allergic reaction to is long: cats and dogs, certain jewelries, different types of soap, specific plants—they can all spark an overreaction of your immune system, sometimes in the form of a rash.

Just a quick refresher: An allergic reaction occurs when your body perceives a harmless substance—such as certain foods, pollen, or pet dander—as a threat. This causes your immune system to overreact in an attempt to keep you safe from that substance, even though it's harmless, per the American Academy of Allergy, Asthma & Immunology (AAAAI). Allergic reactions don't just affect the skin—they can also impact the nose, throat, lungs, ears, sinuses, and stomach lining, per the AAAAI.

But allergy rashes can be uncomfortable and shouldn't be ignored, according to experts. Below, you'll find info on three common types of allergy rashes—eczema, contact dermatitis, and hives—including treatment options and advice on what to do if the rash doesn't go away after treating it.

Atopic dermatitis

Allergy-Rash-Explainer-Eczema-Atopic-Dermatitis

Atopic dermatitis is a type of eczema, which is far more common among children than adults, according to the American College of Allergy, Asthma, & Immunology (ACAAI). It affects up to 20% of children but just 1 to 3% of adults, per the AAAAI, and half of patients who have eczema also suffer from food allergies and hay fever, per the AAAAI. The following are symptoms of eczema, according to the National Eczema Association (NEA):

  • Itchy skin
  • Sensitive skin
  • Dry skin
  • Inflamed skin
  • Discolored skin
  • Rough, scaly, or leathery patches of skin
  • Crusting
  • Oozing
  • Areas of swollen skin

Some people with eczema will experience all of the above symptoms, while others will experience just one or two, according to the NEA. "Eczema [presents as a] persistent, all-over rash," Ronald Purcell, MD, an allergist at Cleveland Clinic, tells Health, adding that it's often caused by a food allergy. But food isn't the only trigger: "Seasonal allergies could certainly cause eczema exacerbation," Kanwaljit Brar, MD, an allergist with advanced training in dermatology at NYU Langone, tells Health.

Where the eczema breakout occurs might depend on the age of the patient, per the AAAAI, which states that the rash usually forms on the knees, elbows, cheeks, and scalp in children, but might also occur on the face, wrists, and neck of adults, in addition to their elbows and knees.

Avoidance of triggers is key in preventing eczema flares, per the AAAAI. A number of treatments are available for eczema patients, and common options include topical moisturizers that lessen itching and topical steroids, which are anti-inflammatory medications that can treat the rash caused by eczema.

Allergic contact dermatitis

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Credit: DermNet NZ

Allergic contact dermatitis is another allergy-related rash, which, as you probably guessed, is caused by coming into contact with an allergen. A number of triggers can cause allergic contact dermatitis, including shampoos, makeup products, and nickel jewelry, Dr. Purcell says. Poison ivy, along with certain fragrances and preservatives are some of the main causes of allergic contact dermatitis, per the Cleveland Clinic.

You may not see a reaction immediately after coming into contact with the product that contains the allergen. In fact, it could take several days after the exposure for the rash to develop. Dr. Brar adds that contact dermatitis is often caused by something you wouldn't consider when thinking about a potential list of allergens, such as "your bed linens, a new piece of furniture in the home, a new pair of shoes, the cleaner you're using for your dishes."

There's also a rare form of contact dermatitis that doesn't require direct contact with the skin to cause a flare, Dr. Brar says. It's called airborne contact dermatitis, occurs when plant resins aerosolize, and can be caused by sunflowers, ragweed, and goldenrod. Airborne contact dermatitis can cause a rash on the face, neck, and eyelids Dr. Brar says.

Contact dermatitis is common, according to the Cleveland Clinic, and individuals with chronic skin problems like sensitive skin might be more prone to the condition. Symptoms of contact dermatitis include

  • Red rash
  • Blistering, oozing, or swollen rash
  • Stinging or burning rash
  • Hive-like rash
  • Painful rash
  • Itchy rash

As with atopic dermatitis, avoiding triggers—if you can identify them—is key in managing allergic contact dermatitis. Other treatments, per the Cleveland Clinic, include topical steroids, oral steroids, and, in severe cases, immunosuppressive medications, which might be recommended if multiple attempts at clearing up contact dermatitis with oral steroids don't work.

Hives

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Credit: DermNet NZ

Environmental allergens like cats and dogs can cause hives, which present as slightly raised, itchy red bumps, Dr. Purcell says. "They're temporary; they go away after exposure is eliminated," he adds. In addition to animals, hives can be caused when your body has an allergic reaction to certain foods and medicines, per MedlinePlus, a resource from the US National Library of Medicine, which lists the following as potential triggers: pollen, insect bites, medicines, animal dander, nuts, eggs, milk, fish, shellfish, and other foods. (FYI: Hives can be the result of causes other than allergens, including emotional stress and excessive perspiration, according to MedlinePlus.)

According to the ACAAI, the symptoms of hives are as follows:

  • Raised itchy bumps that are skin-colored or red
  • Blanching (meaning that, when pressure is applied, the center of the hive will turn white)

Treatment options for hives include antihistamines, steroids, an antibiotic called dapsone that can relieve swelling and redness, an injectable medication called omalizumab that treats chronic hives, and other anti-inflammatory medications, per the American Academy of Dermatology (AAD). If you know cats cause you to break out in hives, and you plan on visiting a friend who has a cat, it might be worth it to consider taking an antihistamine before you arrive at the friend's home, Dr. Purcell suggests. Avoiding triggers that cause hives is also key in managing the condition, he adds.

When should you seek help from a medical professional?

Luckily, rashes caused by allergies can often be treated from the comfort of your own home, and some might clear up as soon as the allergen is removed from your environment. Dr. Purcell says it's important to go see a doctor if your rash doesn't respond to what should work, like topical steroids or taking an antihistamine. Additionally, if you can't figure out what's causing your rash, it might be in your best interest to consult a doctor to figure out what's triggering you so you can avoid the allergen in the future.

If you can, try making an appointment with a skincare specialist, like a dermatologist, rather than visiting an urgent care for help with a rash caused by an allergen, Dr. Brar recommends, explaining that urgent care staff might not always know the best course of treatment and might, for instance, recommend oral steroids when milder treatments would suffice. That said, if you are experiencing any more serious symptoms, like shortness of breath, you should, of course, seek help as quickly as possible, rather than waiting to consult a specialized doctor in the future.

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