What causes hives in a relatively healthy individual after intense physical exertion?

What Causes Hives After a Hard Workout

Hives after intense exercise are caused by exercise-induced urticaria, a form of physical allergy where vigorous physical exertion triggers cutaneous mast cell degranulation and histamine release, resulting in conventional 10-15 mm wheals with pruritus, warmth, and flushing. 1, 2

Primary Mechanism

• Mast cell activation is the fundamental pathophysiologic mechanism, where exercise triggers degranulation of cutaneous mast cells with subsequent release of histamine and other vasoactive mediators into the bloodstream 2, 3
• This occurs only with vigorous physical exertion (jogging, brisk walking, bicycling, racquet sports, skiing, aerobic exercise), not with passive warming like hot baths or saunas, which distinguishes it from cholinergic urticaria 1, 2
• Serum histamine levels increase during symptomatic attacks, confirming the allergic nature of the reaction 2, 3

Critical Cofactors to Identify

Food-dependent triggers are present in approximately 54% of cases, where both exercise AND recent food ingestion (within 4-6 hours) are necessary to produce the reaction 1, 4:

• Common culprit foods include wheat and soy 5
• The same foods can be consumed safely without exercise 1, 4
• Latency periods up to 24 hours after food consumption have been reported 1, 4

Medication triggers occur in 13% of cases 1, 5, 4:

• Aspirin or NSAIDs taken before exercise are the most common pharmaceutical cofactors 1
• Elimination of these medications may enable the patient to tolerate exercise without symptoms 1

Important Clinical Distinctions

Distinguish from cholinergic urticaria, which presents differently 5, 4, 2:

• Cholinergic urticaria produces punctate 1-3 mm wheals (not the 10-15 mm conventional wheals of exercise-induced urticaria) 5, 2
• Triggered by any core body temperature increase, including passive warming 5, 2
• Responds well to hydroxyzine specifically 5, 6

Recognize progression risk to exercise-induced anaphylaxis 1, 5, 4:

• If hives progress beyond isolated skin manifestations to include angioedema, gastrointestinal symptoms, laryngeal edema, or vascular collapse, this becomes exercise-induced anaphylaxis requiring immediate epinephrine 1, 5, 4
• Approximately one-third develop transient loss of consciousness and two-thirds develop upper respiratory obstruction 5, 4
• Symptoms can persist for 30 minutes to hours 1, 4

Predisposing Factors

• Personal or family history of atopy increases risk 1, 4
• The condition represents a form of physical allergy with IgE-mediated mechanisms 1

Common Pitfall

Do not assume all exercise-related hives are the same condition—the size of wheals (1-3 mm punctate vs. 10-15 mm conventional), triggers (any warming vs. exercise only), and systemic progression determine whether this is cholinergic urticaria, exercise-induced urticaria, or exercise-induced anaphylaxis, each requiring different management approaches 5, 4, 2