Difference Between Heat Rash and Allergic Reaction

The key difference between heat rash and allergic reaction is based on their cause. Let us first see, how these two medical conditions occur. Skin is the protective barrier between the body and the outside environment. Sweat glands, which help in cooling the body by perspiration of the sweat, are located in the skin. When the sweat glands are blocked, sweat cannot get to the surface and is trapped in the sweat gland. It causes some inflammations that result in a rash. This is called a sweat rash. In contrast, allergic reactions occur when the body develops an immune-mediated reaction to a harmless environmental agent. Allergy can manifest commonly as urticaria. Urticaria looks like multiple, intensely itchy irregular, large, slightly elevated pale red patches. Allergy can also lead to bronchospasms, anaphylactic shock, and death.

What is Heat Rash?

Heat rashes are common during warm weather where the sweat production is more and sweat ducts can get easily obstructed. It appears all over the body; especially at skin creases. Sweat rash will appear as small reddish, itchy, tiny papules. The symptoms of heat rash are the same in infants and adults. Tight clothing can increase the risk of getting sweat rashes. They do not spread from one person to the other. Sweat rashes are common among infants, elderly and obese people. Good skin hygiene can prevent sweat rashes and resolve of them. The following steps can help to relieve symptoms.

  • Removing or loosening clothing.
  • Let the skin air-dry instead of using towels.
  • Avoid ointments or other lotions which can irritate the skin

What is Allergic Reaction?

An allergic reaction is an immune-mediated reaction to a harmless external agent. Urticaria or hives are the commonest manifestations on allergic rashes. It looks like pale red, raised, itchy bumps. Urticaria appears very quickly upon exposure to the antigenic material and can appear all over the body except palm, soles, and the scalp. These reactions are mediated by mast cells, and Ig M immunoglobulins and is known as Type 1 immune reaction. Treatments are by preventing further contact with the known allergen and administration of steroids and antihistamines. It will take few days for the complete resolution of the rash despite the treatment. Some people have a tendency to develop an allergy to many environmental agents. It is important to get medical advice for urticaria as they can end up with more severe form of allergies such as bronchospasms and anaphylactic shock.

Tissues affected in allergic inflammation

What is the difference between Heat Rash and Allergic Reaction?

Definition of Heat Rash and Allergic Reaction

Heat Rash: An inflammatory skin condition caused due to the obstruction of the ducts in the sweat glands, characterized by the eruption of small red papules accompanied by an itching or prickling sensation.

Allergic Reactions: The hypersensitive response of the immune system to substances called allergens that come into contact with the skin, nose, eyes, respiratory tract, and gastrointestinal tract.

Cause of Heat Rash and Allergic Reaction

Heat Rash: Heat rash is caused by obstructions in the sweat ducts during warm weather.

Allergic Reactions: Allergic reactions are caused by the immune system of the body against harmless environmental agents such as drugs or seafood.

Characteristics of Heat Rash and Allergic Reaction


Heat Rash: Heat rash appears as itchy tiny red dots.

Allergic Reactions: Allergic urticaria appears as itchy, pale red patches.


Heat Rash: Heat rash appears slowly over hours to days.

Allergic Reactions: Urticaria can appear within minutes.


Heat Rash: Heat rashes can rarely get infected.

Allergic Reactions: Urticaria can progress to anaphylactic shock.


Heat Rash: Heat rash needs good skin hygiene.

Allergic Reactions: Urticaria needs a short course of steroids and antihistamines.


Image Courtesy:

“Miliaria rubra mild” by Sentient Planet – Own work. (C BY-SA 3.0) via Commons

“Tissues Affected In Allergic Inflammation” by SariSabban – Sabban, Sari (2011), The University of Sheffield.(CC BY-SA 3.0) via Commons