Can allergies cause a skin rash?

How allergies cause it

Skin can become allergic to things it touches. In allergic contact dermatitis, skin contact with a specific material triggers an immune response that shows up as a rash.¹ Unlike classic allergic reactions, which are driven by the IgE antibody, it does not involve IgE.³

Contact dermatitis can develop right away, or it can occur after months of exposure to a substance.³ Allergic contact reactions can develop 24 to 48 hours after contact, and once a reaction starts, it may take 14 to 28 days to go away.¹ The most common example is the itchy, red, blistered reaction after touching poison ivy. Other substances that frequently cause it include metals such as nickel, cosmetics that contain fragrances and preservatives, hair dyes, and rubber (latex) products.¹ Some allergens cause a skin reaction only when the skin is also exposed to sunlight.⁵

Contact dermatitis causes redness, itching and sometimes small bumps.⁴ ACAAI says its symptoms can also include blisters and burning.⁵

Allergies cause other rashes too. Hives are red, itchy welts or bumps that don’t usually last long, and hives that last less than six weeks are usually caused by an allergic reaction or a viral infection.⁶

Eczema and allergies

Atopic dermatitis, often called eczema, is a chronic disease that causes inflammation, redness and irritation of the skin.⁷ Its most common symptom is itching, which can be severe.⁷ AAAAI calls eczema the most common skin condition, especially in children.²

Eczema and allergies often travel together. Eczema is often linked with asthma, hay fever or food allergy.² Still, no one knows what causes atopic dermatitis. Researchers know that changes in the skin’s protective layer can cause it to lose moisture, leading to dryness, damage and inflammation, and that changes in genes, problems with the immune system and exposure to certain things in the environment may contribute to those changes.⁷

Allergens can make eczema worse. Potential triggers include animal dander, pollens and dust mites, along with sweating, infections, stress and irritants such as wool or soaps.¹ Foods are not common triggers of eczema, except rarely in infants and young children.¹

Allergies or something else?

Not every contact rash is an allergy. In irritant contact dermatitis, a material damages the skin at the point of contact because the chemical is caustic, not because of an immune response.¹ It is often more painful, burning or stinging than itchy, and it commonly appears on the hands, often from materials touched at work.¹

Where the rash sits is a clue. You get a contact rash where you have touched an irritant, such as a chemical, or something you are allergic to, like poison ivy.⁴

A rash can also come from an infection. ACAAI says that if you have a fever along with a rash, you should talk to your doctor about possible bacterial or viral infections.⁶ Eczema itself is not contagious.⁷

When to see a doctor

MedlinePlus says to see your health care provider if a rash is bad, if it does not go away, or if you have other symptoms.⁴ AAAAI notes that eczema that weeps, or leaks fluid that crusts over when scratched, is also infected.²

An allergist may use tests such as a patch test to identify the allergen responsible for a rash.¹

Call 911 if you have hives along with fainting, shortness of breath, tightness in your throat, tongue or face swelling, or wheezing.⁸