Allergic Contact Dermatitis is a form of eczema caused by an immune reaction to chemicals that have come in contact with the skin or which are ingested and cause a systemic reaction that can also affect the skin. The immune system must encounter a chemical at least once to become immune, or allergic to it. Very often you will become allergic to something that you have been using or exposed to for years. This means that if you’ve been using something for 20 years, you can still become allergic to it–and this actually happens quite frequently.
What Areas of the Body Does it Affect?
Any area of the body can develop allergic contact dermatitis. Here are some of the most common:
Scalp: Some of the more common culprits for allergic contact dermatitis on the scalp include a carcinogenic chemical from hair dye called paraphenylene diamine. Also very common are fragrances and formaldehyde-releasing preservatives—these allergic reactions often manifest as a pink, scaly and itchy rash around the hairline—often on the upper part of the back of the neck and around the back side of the ears.
Neck: Can also be a location where hair care products cause an allergic reaction. Other common reactions are to nickel and cobalt in costume jewelry. In this case, the allergy usually manifests where the jewelry touches, but often is not as symmetrical as you would think it would be.
Trunk: Clothing dermatitis is a common problem with allergies to azo dyes used to color the fabrics. Also common is formaldehyde and formaldehyde-releasing preservatives that are used to “finish” fabrics and to make them “no-iron” or “permanent press”. This allergic reaction often manifests as a scaly pink rash around the front of the armpits and the upper, inner thighs where clothing rubs the most. Azo dyes that are used to color fabrics (think dark blues and blacks) are a common culprit in clothing dermatitis.
Hands: Please see our section on Hand Dermatitis.
Perianal Skin: The preservatives that are used in baby wipes very commonly cause an embarrassing allergic reaction with an itchy rash around the perianal skin. A preservative called methochloroisothiazolinone/methylisithiazolinone, or MCI/MI has been reported to cause allergic contact dermatitis from baby wipes. Other common allergens present in baby wipes include tocopheryl acetate, petrol-based propylene glycol, fragrances, 2-bromo-2-nitropropane-1,3-diol, and carbamates. Allergic contact dermatitis from baby wipes can present as a red, irritated bottom in children OR in adults who use baby wipes for grooming purposes. It can manifest anywhere they are used-eczema around the eyes if you use baby wipes to remove your makeup, hand dermatitis in mothers of young children who use baby wipes (usually manifests more at the fingertips as dry, cracked, blistery fingertips), or it can also occur around the anus if baby wipes are used after going to the restroom.
Vulvar or Penile Skin: Itching of the vulvar or penile skin can be the result of many different conditions. Very commonly however, an allergic contact dermatitis in these areas can occur as a result of any of the above chemicals that are listed under perianal skin. Additional chemicals can often be the culprit too; allergy to latex in condoms, to the lubricants or fragrances in condoms and to the preservatives found in vaginal lubricants (allergy to benzalkonium chloride is especially common in vaginal lubricants) or to fragrances or tocopherols used in maxi pads or douches. More and more commonly, products meant to be used on this delicate skin include essential oils. While essential oils may have a therapeutic place in some conditions, they should not be applied to penile or vaginal skin as they are extremely common and potent contact allergens. Less common, but common enough to mention it, is allergy to neoprene from bicycle seats (and from the latex in bicycle shorts), exercise mats and yoga mats.
In addition to an allergic reaction to a chemical, itching or rash of the vulvar or penile skin in this area has several causes. Common causes include infection with Candida, Gonorrhea, Trichomonas, Chlamydia, or Syphilis. It can be due to autoimmune diseases like lichen planus, lichen sclerosus, psoriasis, seborrheic dermatitis and more. Itching in this area can also be nerve-related; where a nerve in the area has been damaged or pinched from some sort of trauma (an accident or even childbirth). In general, Most-commonly however, vulvar and penile itching is caused by an allergic reaction to one of the chemicals listed above.
In general, if you have a vaginal itching problem and you do not have a yeast infection or any other infection, and the skin is bright red or pink but looks normal otherwise, one should eliminate all possible allergens from this area (including soap—you don’t need soap down here) and see if it heals up. If not, consult with a dermatologist who is both experienced and comfortable in assessing this problem. I recommend you call the office that you are considering going to and asking the receptionist if the doctor has experience in this area. Frankly, there are few dermatologists who feel comfortable in treating this condition.
Ankles & Shins: If you have eczema in these areas and it has not been present since birth or early childhood (think atopic dermatitis) and is symmetrical, then consider allergy to latex (from socks), azo dyes (used to dye socks and clothing), neoprene and nitrile (sports pads—soccer, rugby, lacrosse, football etc.), formaldehyde (used to finish fabrics and to make them permanent press though the rash from this allergy is more common on the upper/inner thighs and the anterior armpits). If you suspect that you may have an allergy to a chemical in this area and you cannot figure it out, consult with a member of the American Contact Dermatitis Society for patch testing; a group of dermatologists who have special training in this technique and who do the type of allergy testing that is needed to diagnose a particular chemical allergy.
Feet: Allergic contact dermatitis on the feet is often due to latex (socks and shoes), chromates (in shoes), epoxy glues (in shoes) and to the fragrances or preservatives contained in skin care products that are used on the feet.