What is the management approach for a patient with a known allergy to henna?

Management of Henna Allergy

The cornerstone of henna allergy management is strict avoidance of all henna-containing products and para-phenylenediamine (PPD), combined with prescribing epinephrine auto-injectors for patients with prior systemic reactions, followed by allergist referral for comprehensive testing and cross-reactivity evaluation. 1

Immediate Assessment and Allergen Identification

Determine the Type of Henna Exposure

• Identify whether the patient was exposed to pure henna (lawsone) or "black henna" containing PPD, as the vast majority of allergic reactions are caused by PPD additives rather than pure henna itself. 2, 3
• Pure henna (red henna) has very low allergic potential with rare instances of contact allergy, while black henna causes contact allergy to PPD at an estimated frequency of 2.5%. 3
• Document the timeline of reaction onset, as PPD-induced allergic contact dermatitis typically manifests within 48-72 hours after exposure. 4, 5

Assess Reaction Severity

• For localized contact dermatitis without systemic symptoms: Treat with topical corticosteroids (betamethasone or mometasone furoate 0.1% cream) and oral antihistamines. 6, 4
• For severe reactions with facial swelling or blistering: Administer oral corticosteroids (prednisone 1 mg/kg daily, maximum 60-80 mg) for 2-3 days. 7, 4
• For any history of systemic allergic reaction or anaphylaxis: Prescribe epinephrine auto-injectors (two doses) with hands-on training immediately. 1, 7

Acute Treatment Protocol

For Active Contact Dermatitis

• Apply topical corticosteroid (mometasone furoate 0.1% or betamethasone cream) to affected areas twice daily. 6, 4
• Administer oral antihistamines for pruritus control (diphenhydramine 25-50 mg every 6 hours or equivalent H1-antihistamine). 7, 4
• For severe blistering or extensive involvement, prescribe oral prednisone 50 mg daily for 3 days (or 1 mg/kg daily for children). 7, 4
• Monitor for secondary bacterial infection (particularly Staphylococcus aureus) and treat with dicloxacillin if superinfection develops. 6

For Systemic Reactions or Anaphylaxis

• Administer epinephrine 0.3-0.5 mg intramuscularly (1:1000) into the anterolateral thigh immediately, repeating every 5-15 minutes as needed for persistent symptoms. 1, 7
• Position patient supine with legs elevated unless respiratory distress is present. 7
• Establish IV access and administer crystalloid bolus (500-1000 mL for adults, 20 mL/kg for children). 7
• Add H1-antihistamine (diphenhydramine 25-50 mg IV) and H2-antihistamine (ranitidine 50 mg IV or famotidine 20 mg IV). 7
• Consider methylprednisolone 1-2 mg/kg IV every 6 hours to prevent biphasic reactions. 7
• Observe for minimum 4-6 hours after symptom resolution, with longer observation for severe reactions. 7

Comprehensive Avoidance Strategy

Primary Allergen Avoidance

• Instruct complete avoidance of all henna products, including hair dyes, temporary tattoos, and cosmetic applications. 1, 3
• Emphasize that "natural" or "pure" henna may still contain PPD additives, and black henna should be avoided entirely. 2, 3, 4
• Educate that even a single prior exposure to black henna can cause sensitization, leading to severe reactions upon re-exposure. 4, 5

Cross-Reactive Substances to Avoid

• Hair dyes containing PPD and related compounds (diaminotoluenes, diaminobenzenes) must be avoided, as cross-reactivity is common. 3, 4
• Local anesthetics (benzocaine, procaine) may cross-react with PPD. 3
• Textile dyes used in dark-colored clothing may cause reactions in sensitized individuals. 3
• Rubber chemicals and certain industrial dyes can trigger cross-reactions. 3

Special Populations

• For children with glucose-6-phosphate dehydrogenase (G6PD) deficiency, even pure henna application can cause life-threatening hemolysis and must be strictly avoided. 3
• Warn adolescents and young adults that PPD sensitization may have important consequences for future career prospects in industries using hair dyes or textile dyes. 3

Follow-Up and Specialty Referral

Allergist Referral (Essential)

• Refer all patients with henna allergy to an allergist/immunologist within 1-2 weeks for comprehensive patch testing and cross-reactivity evaluation. 1
• Patch testing should include PPD 1% in petrolatum, standard European battery, and pure henna powder to differentiate between PPD allergy and true henna allergy. 4
• Testing helps identify the specific trigger and guides avoidance of cross-reactive substances. 1

Patient Education Materials

• Provide written information about allergen identification and avoidance strategies using the SAFE mnemonic (Seek support, Allergen identification and avoidance, Follow up with specialty care, Epinephrine for emergencies). 1
• Educate patients to read product labels carefully and inquire about ingredients in hair salons and cosmetic facilities. 1
• Direct patients to reliable resources such as the American Academy of Allergy, Asthma and Immunology (www.aaaai.org) and American College of Allergy, Asthma and Immunology (www.acaai.org). 1

Discharge Planning and Long-Term Management

Prescription Bundle for Patients with Systemic Reactions

• Two epinephrine auto-injectors with demonstration of proper use technique. 1, 7
• Prednisone 1 mg/kg daily (maximum 60-80 mg) for 2-3 days. 7
• H1-antihistamine for ongoing symptom control. 7
• H2-antihistamine (ranitidine or famotidine) twice daily for 2-3 days. 7
• Written anaphylaxis action plan with clear instructions on when to use epinephrine. 7

Monitoring and Prevention

• Advise patients to check epinephrine auto-injector expiration dates annually and ensure the liquid remains clear. 1
• Instruct patients to carry epinephrine at all times and to use it at the first sign of systemic symptoms, then immediately call emergency services. 1
• Recommend medical alert jewelry identifying henna/PPD allergy for patients with history of severe reactions. 1

Critical Pitfalls to Avoid

• Never assume "natural henna" is safe—most commercial henna products contain PPD additives that cause the majority of allergic reactions. 2, 3, 4
• Do not delay epinephrine administration in patients with systemic symptoms; antihistamines and corticosteroids are adjunctive only and do not treat acute anaphylaxis. 1, 7
• Avoid treating facial swelling from delayed hypersensitivity as angioedema—this is type IV hypersensitivity requiring corticosteroids, not epinephrine or antihistamines alone. 5
• Do not discharge patients with systemic reactions without epinephrine auto-injectors and allergist follow-up arranged—these patients are at risk for repeat episodes. 1, 7
• Screen for G6PD deficiency in children before any henna exposure, as even pure henna can cause fatal hemolysis in this population. 3