It is a common scenario to want to self treat an unexplained rash  before going to the doctor. Maybe you scratch it and it gets irritated and to be on the safe side you go to your medicine cabinet and grab an over the counter antibiotic cream. You put it on your rash to avoid infection. But you soon find that your rash looks worse than it did before. What could be going on? It just may be that you have an allergy to Neomycin.

What is neomycin?

According to the American Academy of Dermatology neomycin is a very common allergen found in both prescription and over the counter topical antibiotic creams, ointments, lotions, ear drops, and eye drops. This medication is also sometimes used in combination with topical steroids.

How common is an allergy to neomycin?

It is very common. In the recent 2010 July/August issue of Health magazine it was reported that neomycin is the fifth most common skin allergen and that ten percent of people with suspected allergic-skin disease are actually allergic to neomycin.

In fact, it was also reported on MD Consult, an on-line reference for physicians,  that the American Contact Dermatitis Society has named neomycin as “The Allergen of the Year for 2010.” Although it is such a common allergy, many people don’t realize they are allergic to it.

How will my skin react if I am allergic to neomycin?

An allergy to neomycin will produce what is known as contact dermatitis. Contact dermatitis is when the skin becomes irritated and inflamed due to direct contact with an allergen. People having an allergy to neomycin may develop an inflamed weepy rash if there is prolonged exposure as in repeated use of products containing neomycin. It is important to note that a skin reaction may not develop right away and can take a week or more to develop.

In an MD Consult article entitled, “Neomycin named allergen of the year” it was reported that “Dermatitis from neomycin often develops 7 days or more after exposure.”

If you want to see what a skin reaction can look like, The New Zealand Dermatological Society web site has images of neomycin allergic reactions.

Who is more at risk of having this allergy?

People with a history of any type of allergy are more at risk for developing contact dermatitis in general. People who suffer from atopic dermatitis or eczema, may be more sensitive to neomycin. One typical scenario is that the eczema sufferer will use a topical combination of neomycin and corticosteroids only to find that their condition is not improving. An allergy to neomycin may be the cause or even an allergy to cortisone creams.

How is an allergy to neomycin diagnosed? Most commonly a patch test is used to diagnose a neomycin allergy. During a patch test, possible allergens are taped to the skin for 48 hours. The doctor then examines the skin in 24 hours and then again after 48 hours. Sometimes an intradermal test may be used where they will inject a small amount of the suspected allergen under the surface of the skin and check afterward for a reaction. A positive reaction from the intradermal test will look similar to a positive reaction from the patch test. A small hive with redness and swelling will appear.