What are the skin manifestations of allergic reactions?

Skin Manifestations of Allergic Reactions

The skin is involved in approximately 80-90% of allergic reactions, with urticaria (hives), angioedema, flushing, and pruritus being the most common cutaneous manifestations, though critically, 10-20% of severe anaphylactic reactions occur without any skin findings at all. 1

Primary Cutaneous Manifestations

Immediate-Type Reactions (IgE-Mediated)

Urticaria (Hives):

• Raised, pruritic wheals with central swelling and surrounding erythema that blanch with pressure 2, 3
• Individual lesions typically resolve within 1-24 hours, though new lesions may continue to appear 3
• Can be generalized or localized, and represents the most common skin manifestation in food-induced allergic reactions (40-60% of cases) 4
• Intense pruritus typically appears within minutes to 2 hours of allergen exposure 5

Angioedema:

• Deeper dermal and submucosal swelling affecting the lips, eyelids, tongue, uvula, and mucous membranes 1, 5
• Less pruritic than urticaria; patients more commonly report pain or burning 3
• Resolves more slowly than urticaria, usually within 72 hours 3
• Critical warning: Angioedema involving the lips, oral cavity, or throat combined with any respiratory or cardiovascular symptoms constitutes anaphylaxis and requires immediate epinephrine administration 5

Flushing and Pruritus:

• Generalized erythema with warmth, often accompanied by intense itching 1
• May occur without discrete wheals 1
• Pruritus can involve the throat, external auditory canals, palms, and soles 1

Contact-Mediated Reactions

Contact Urticaria:

• Immediate wheal-and-flare reaction at the site of direct skin contact with allergen 4
• Can progress to systemic symptoms (contact urticaria syndrome) 4
• Common with occupational exposures (e.g., latex, foods in food handlers) 4

Protein Contact Dermatitis:

• Eczematous reaction caused by direct contact with food proteins 4
• Classic example is baker's eczema from flour exposure 4

Delayed-Type Reactions

Maculopapular Rash:

• Most common delayed cutaneous drug reaction, presenting as erythematous, widespread lesions 5
• Usually mild but can progress to severe reactions 5

Atopic Dermatitis Exacerbation:

• Food allergens can trigger or worsen atopic dermatitis, particularly in infants and young children with moderate-to-severe disease 5, 6
• Approximately one-third of children with moderate-to-severe atopic dermatitis have food allergies 5
• Common food triggers include cow's milk, eggs, wheat, soy, peanut (in young children); tree nuts, shellfish, fish (in older children) 6

Critical Recognition Points

When Skin Findings Indicate Anaphylaxis

You must recognize anaphylaxis when skin manifestations occur with:

• Any respiratory compromise (dyspnea, wheeze, stridor, throat tightness) 1
• Any cardiovascular symptoms (hypotension, syncope, dizziness, tachycardia) 1
• Persistent gastrointestinal symptoms (cramping, vomiting, diarrhea) after allergen exposure 1

Red Flags for Severe Reactions

Immediate epinephrine and emergency management required when you observe: 5

• Mucosal involvement (swollen lips, oral edema, throat tightness) with respiratory or cardiovascular symptoms
• Progressive symptoms: blistering, exfoliation, widespread urticaria with rapid onset
• Skin changes accompanied by dyspnea, tachycardia, or blood pressure changes
• Bronchospasm, hypoxia, or cardiac problems

Critical Pitfall to Avoid

The absence of skin manifestations does NOT rule out anaphylaxis. 1, 7

• 10-20% of anaphylactic reactions, including fatal cases, present without any cutaneous findings 1
• Severe episodes with rapid cardiovascular collapse can occur without skin manifestations 7
• Never delay epinephrine administration while waiting for skin findings to appear 1

Additional Cutaneous Findings in Anaphylaxis

Beyond the primary manifestations, you may observe: 1

• Morbilliform rash
• Conjunctival erythema and injection
• Paleness or cyanosis
• Periorbital edema

Documentation and Follow-Up

Document all allergic rashes as drug allergies in the medical record to prevent future re-exposure, as even mild reactions can progress to severe anaphylaxis upon rechallenge. 5

• Cross-sensitivity between related drugs has been documented, requiring caution when switching medications 5
• Consider allergy testing (skin prick testing or serum-specific IgE) for confirmed reactions to guide future management 1, 6