Contact Dermatitis

Irritant vs allergic contact dermatitis

Common triggers

Irritants

• frequent handwashing and "wet work" (health care, cleaning, hairdressing, food service, caring for babies)
• soaps, detergents and cleaning products
• solvents, oils, cement and industrial chemicals
• saliva (lip-licking dermatitis), urine and stool (diaper rash)
• friction and occlusion, such as under gloves

Allergens

• Nickel: jewelry, belt buckles, jeans buttons, watch backs, phones. The most common contact allergen
• Fragrances in perfumes, cosmetics, soaps and household products
• Preservatives: methylisothiazolinone, formaldehyde releasers in shampoos, wipes and creams
• Hair dye: paraphenylenediamine (PPD), also in black henna tattoos
• Rubber accelerators in gloves and shoes, and latex
• Topical medicines: neomycin, bacitracin, some anesthetic creams, and occasionally hydrocortisone itself
• Plants: poison ivy, poison oak and poison sumac (urushiol oil), causing streaks of blisters
• Acrylates in artificial nails and nail glue
• Light-triggered reactions: some sunscreens, fragrances and plants cause rashes only after sun exposure (photodermatitis)

Symptoms

• red, itchy rash where the skin touched the substance
• burning or stinging, especially with irritants
• dry, scaly, cracked skin in chronic cases
• swelling, especially around the eyes, face and genitals
• small or large blisters that may ooze and crust (common in poison ivy and acute allergy)
• darkened, thickened skin after long-term scratching

The location gives clues: earlobes and wrist (nickel jewelry), eyelids (nail polish, makeup, transferred from hands), scalp and hairline (hair dye), hands (work and gloves), feet (shoes), and face (cosmetics).

Diagnosis

Contact dermatitis is diagnosed from the appearance and pattern of the rash and a careful history of exposures at home, at work and in hobbies. Doctors may rule out other causes such as eczema, psoriasis and fungal infection.

Patch testing identifies the cause of allergic contact dermatitis. Small amounts of common allergens are taped to the back for 48 hours, then read at 48 hours and again around 72 to 96 hours. Avoid getting the back wet and avoid sun exposure on the back during testing. It is recommended when the rash is persistent, recurrent or the trigger is unclear.

Treatment

Avoid the trigger

This is the most important step. Once you know the cause, check product labels, choose fragrance-free and hypoallergenic products, and use substitutes (for example nickel-free jewelry or nitrile gloves instead of latex).

Soothe and repair the skin

• wash the area gently with water after contact, especially within minutes of poison ivy exposure, along with clothes, tools and pet fur
• apply fragrance-free moisturizers or ointments often, especially after handwashing
• cool compresses for weeping, blistered skin
• over-the-counter 1% hydrocortisone for small, mild patches, following the label

Prescription treatment

• Stronger topical steroids for 1 to 3 weeks, chosen by body site
• Calcineurin inhibitor creams (tacrolimus, pimecrolimus) for the face and eyelids
• Oral steroids for severe or widespread reactions, such as extensive poison ivy, usually tapered over 2 to 3 weeks to prevent rebound
• Antihistamines may help sleep, but itch in contact dermatitis is not mainly driven by histamine

Hand dermatitis

• wear cotton-lined protective gloves for wet work, and limit glove wearing time
• use lukewarm water and soap-free cleansers
• apply a thick barrier cream before work and moisturizer after every wash
• alcohol hand rubs may sting cracked skin but are often less damaging than repeated soap washing

Outlook

Most cases clear within 2 to 4 weeks once the trigger is avoided. Allergic sensitivity is usually lifelong, so re-exposure will cause the rash again. Chronic hand dermatitis can affect work and may need occupational health input.

Frequently asked questions

What is the difference between allergic and irritant contact dermatitis?

Irritant contact dermatitis is direct damage to the skin from substances like soap and water and can affect anyone. Allergic contact dermatitis is an immune reaction to a specific substance, such as nickel or fragrance, appearing 1 to 3 days after contact in people who are sensitized.

How long does contact dermatitis last?

Once the trigger is removed, most rashes improve within days and clear within 2 to 4 weeks. Poison ivy rash typically lasts 1 to 3 weeks. Repeated or ongoing exposure keeps it going.

How do you find out what is causing contact dermatitis?

A careful history of what touches your skin at home and work often identifies irritants. Patch testing by a dermatologist or allergist identifies specific allergens such as nickel, fragrances, preservatives and rubber chemicals.

What is the best treatment for contact dermatitis?

Avoiding the trigger, moisturizing and using a topical steroid of the right strength for the body area work for most people. Severe or widespread reactions may need oral steroids. Patch testing helps prevent recurrence.

Is contact dermatitis contagious?

No. It cannot spread from person to person. Poison ivy oil (urushiol) can transfer from clothing, pets or tools to skin, but the rash fluid itself does not spread the rash.