Coin-shaped eczema: nearly half of patients reacted to an allergen like nickel

If you have round, itchy patches of eczema that keep coming back, you now have a clear place to look: what touches your skin. A new review found that nearly half of people with coin-shaped eczema, called nummular eczema, reacted to at least one contact allergen on a patch test.

Nickel was one of the most common culprits. So were fragrance, leather chemicals and a few others you can check for at home. That is useful news, because an allergen you can spot is an allergen you can avoid.

How the study worked

Researchers searched three medical databases on April 30, 2026, for studies that used patch testing in people with nummular eczema. Of 287 studies they found, 10 observational studies met the requirements, and the results were published in October 2026 in the Journal of Drugs in Dermatology. Because those studies used different patch test methods, the review shows that these allergies are common in this eczema, and future research will sort out exactly how they fit in.

What they found

Across the studies, the typical share of people who reacted to at least one allergen was 47.8%. That is nearly half. Results ranged from 26.7% to 56.0% depending on the study, so in some groups it was about one in four people and in others just over half.

The allergens that came up most often were:

• Nickel and nickel sulfate, the metal found in many jewelry pieces and belt buckles
• Potassium dichromate, found in leather and cement
• Cobalt chloride
• Fragrance mix
• Neomycin, an antibiotic
• Colophony, a natural resin
• Formaldehyde
• Paraphenylenediamine, found in hair dyes
• Rubber-related chemicals

There was a second finding worth knowing. Among the studies that reported it, a typical 33.5% of people with nummular eczema also had allergic contact dermatitis, either now or in the past. That is about one in three. Allergic contact dermatitis is a skin rash caused by touching something you are allergic to.

What is a patch test?

A patch test is a simple way to find out what your skin reacts to. A dermatologist places small amounts of common allergens on your skin, usually on your back. You wear them for a few days, and then the doctor checks which spots turned red or itchy.

The review supports this test for people whose nummular eczema is severe or does not improve with treatment. If that sounds like you, a patch test can point to the specific allergens to avoid. Avoiding them can help you keep the eczema under control and rely less on medicines.

What you can do today

You do not need a test to start looking for clues. Take a few minutes and go through the things that touch your skin every day:

• Read the ingredient list on your soap, body wash and moisturizer. If you see “fragrance,” put a fragrance-free version on your shopping list.
• Look at your jewelry, watch, belt buckle and any metal that rests against your skin. Nickel is a common trigger.
• Think about leather items and anything new you started using before your last flare.
• Keep moisturizing every day.

Then add one simple habit: next time a patch flares, jot a quick note on your phone about what touched that spot in the last day or two. After a few weeks you will have a pattern to show your dermatologist if you decide to ask about patch testing.

Start with the soap and moisturizer labels this morning. It takes two minutes, and it is the easiest swap on the list.