3-2-1 Contact!

Almost daily, I see someone with an itchy rash from something they came into contact with that has irritated the skin.  This condition is called, fittingly, contact dermatitis.  Figuring out what caused the rash requires a little bit of detective work.  Luckily, the location of the rash can often give some clues:

Eyelid rashes: the most common causes are nail polish (especially containing formaldehyde) and acrylic nails (the glue contains ethyl methacrylate or methyl methacrylate).  Also makeup/cosmetics (preservatives like methylchloroisothiazinolone and imidazolidinyl urea) can irritate the eyelids.  Contact solution containing thimerosal is a common culprit.

Earlobes and belly buttons/abdomen rashes are often caused by items containing nickel, the most common allergen.  This includes costume jewelery, belt buckles, and metal snaps/fasteners that rub against the skin.  Kids with eczema/atopic dermatitis (see my previous post- Itchin' An A Scratchin'- to learn about this condition) often have nickel allergy.  Parents can sew patches on the inside of pants to keep the metal parts from coming into contact with skin. Test before you wear: a chemical called dimethylglyoxime can be painted on a metal object and will turn pink if it contains nickel.

Hand contact dermatitis often varies based on profession and hobbies.  People who wear gloves often have allergies to latex and rubber.  A fun fact: people allergic to latex may also be allergic to avocado, bananas, chestnuts, and kiwi.  Dentists and surgeons can get rashes from ethyl methacralate.  Cleaning agents can contain preservatives that release formaldehyde.  (Aside from the fact that frequently wetting hands will cause irritation in general).  Hobbies, like building model planes and cars, can expose you to glues.

Foot contact dermatitis may be caused by the rubber in shoes (mercaptobenzothiazole) or the leather portion (chromates).  The rubber part along the top of socks may cause a contact dermatitis on the shins.

Scalp contact dermatitis may be due to hair dyes containing para-phenylenediamine.  This chemical is found in henna tattoos (this is what makes the tattoo have that black color instead of the traditional reddish-brown), and people can get rashes from those, too. 

One of the most common allergies is to neomycin.  This is found in topical antibiotic creams or first-aid creams, ear drops, and nose drops.  Often people are also allergic to bacitracin as well.

And the list doesn't stop there.  People can be allergic to fragrances, lanolin, tape adhesive, plants, and medications.  If the cause of the contact dermatitis isn't obvious, patch testing can be performed by the dermatologist, where the most common allergens are taped on the back and then removed a few days later to look for a reaction.  Learning what allergens to avoid can make all the difference!