Causes of Itch During Exercise

Most itches are not problematic and will often have no recognizable cause. However, in some cases, an itch will develop whenever you engage in strenuous physical activity, such as exercise. While annoying, it is rarely serious and will usually resolve soon after you finish working out.

There are cases, though, where an itch can become so intrusive that it interferes with your ability to exercise. At other times, a sudden acute itch may be the first sign of a potentially life-threatening condition known as exercise-induced anaphylaxis (EIA).

What Is an Itch?

An itch, also known as pruritus, is a general sensation arising from the irritation of skin cells or nerve cells associated with the skin. The sensation occurs when nerve endings, called proprioceptors, are stimulated by infection, injury, chemicals, temperature, or the body's own immune response.

When proprioceptors are stimulated, they deliver messages to the brain and spinal cord which, in turn, trigger scratching or rubbing reflex. Scratching interferes with these nerve signals, providing transient relief, but also serves as a warning sign of an abnormal physical condition.

Pruritus may or may not be accompanied by physical symptoms, such as a rash or hives. The itch may either be localized (constrained to a specific region) or generalized (occurring over most or all of the body).

Allergies and Itching

An itch that occurs exclusively during exercise is most often associated with some form of allergy. An allergy is an abnormal immune response by which the body releases inflammatory chemicals (called histamine) in response to an otherwise harmless stimulus (called an allergen).

Depending on what you are allergic to, you may experience itching and other symptoms affecting the eyes, nose, throat, lungs, skin, or gastrointestinal tract. The allergy may be triggered by something you come into contact with during exercise, something you inhale or ate at the gym, or a sudden change in environment.

Among the examples:

• Contact dermatitis is a skin rash caused by something you come into physical contact with. The rash tends to be mild to moderate in severity and, in some cases, may be felt more than seen. Latex (used in yoga mats and sports bras) and spandex (found in athletic wear) are common allergens. Other possible culprits include body sprays, powders, or lotions you apply before or after exercise.
• Inhalant allergies are those caused by substances you breathe in. While pollens are a common cause, any substance you can inhale can trigger an allergic response. These include fungi found in locker rooms, disinfectants used to clean the gym, or deodorants used by others. Inhalant allergies can usually be identified by the development of nasal symptoms.
• Food allergies can occur in response to any food you eat but are especially common with certain fruits and nuts. Allergies like these may cause the transient swelling of the lips, tongue, and throat. Other may cause generalized itchiness and rash. Possible culprits at the gym include protein bars (which may contain hidden nuts) and energy drinks (in which a caffeine allergy may be amplified by exercise).

Depending on the cause, an allergy may be treated with an over-the-counter  antihistamine. Other cases may require a topical, oral, or injected corticosteroid.

Non-Allergic Itching

There are other conditions that can cause pruritus or itching during exercise. Some are similar to an allergy in that they involve the release of histamines, while others have no association at all.

Two such examples include:

• Heat rash, also known as prickly heat and miliaria, develops when perspiration becomes trapped in the sweat pores. This can lead to the formation of superficial blisters or bumps. Heat rash tends to occur during strenuous activity in extreme temperatures (such as running under the midday sun).
• Cholinergic urticaria is a condition in which increased body temperatures trigger the swelling of the skin and the formation of hives. While similar to an allergy, urticaria involves a different mechanism by which immune cells, called mast cells, spontaneously break apart and flood the body with histamine. While the exact cause of exercise-induced urticaria is unclear, it may be spurred by an underlying food allergy which is amplified by exercise. Despite this association, urticaria is not classified as an allergy.

By removing yourself from the heat and lowering your body temperature, both conditions tend to resolve on their own. Longer-lasting hives may benefit from a short course of oral antihistamines.

Exercise-Induced Anaphylaxis

In rare circumstances, an exercise-related allergy or urticaria can spur a life-threatening, all-body reaction known as exercise-induced anaphylaxis (EIA). Symptoms of anaphylaxis include:

• Hives
• Facial swelling
• Swelling of the tongue and throat
• Wheezing
• Shortness of breath
• Irregular and/or rapid heart rate
• Cold and clammy skin
• Diarrhea
• Abdominal cramps
• Dizziness
• Nausea and vomiting
• Confusion

An emergency injection of epinephrine (adrenaline) is often needed to counter the allergic response. Intravenous antihistamines or corticosteroids may be used to decrease inflammation in the air passages.