If you have a rash on your hands — or elsewhere on your body — the cause may be obvious. You were hiking and touched some poison ivy, for example, or you were bitten by insects. But a skin condition like eczema, which often occurs on the hands, may have a cause that’s trickier to identify.
Simply looking at your rash won’t always be enough even for a specialist like a dermatologist to determine what triggered your symptoms. With more than 15,000 known skin allergens out there, your doctor may need help identifying the culprit behind your condition. Enter the patch test.
A patch test involves placing adhesive patches on your skin, usually on your back. The FDA has approved only one such test: the TRUE (thin-layer rapid use epicutaneous) test, which contains small amounts of 35 common allergens on three patches.
Once they’re placed, you’ll wear the patches for a couple of days before returning to your doctor. If your skin reacts to the patch, that’s evidence that one of the allergens is to blame for your condition. If your skin does not react, your doctor can widen the search with additional patch tests that can identify different allergens.
If you have hand eczema, a patch test may reveal the allergen or allergens that trigger your symptoms. Avoiding any such allergens is critical for preventing flare-ups.
What Types of Hand Eczema Can a Patch Test Benefit?
Eczema, a condition that causes dry, itchy, and bumpy patches on your skin, can affect your hands. In fact, hand eczema — sometimes referred to as hand dermatitis — is one of the most common types of eczema.
There’s more than one type of eczema. Some of them have a genetic cause that you’re born with, and some have causes that remain unknown. Two types, though, have causes that often can be identified with a patch test.
Irritant contact dermatitis is the most common type of eczema, and it can affect your hands. It’s caused when your skin comes into contact with things that irritate the skin, such as the harsh chemicals used in certain occupations. Hairdressers and nail technicians, for example, have a high risk of it.
Allergic contact dermatitis is caused by allergens in your environment that have penetrated your outer layer of skin. They can provoke an immune response if your immune system identifies them as a threat. Over time, your exposure to these allergens can lead to it. Nickel, a metal often used in jewelry, is a common allergen, as are ragweed pollen and some fragrances, such as ones found in scented products.
Experts consider patch testing the gold standard for diagnosing allergic contact dermatitis, and it also can aid in identifying on-the-job irritants that may be responsible for your hand eczema.
Hand eczema can be acute. That means you’ll have it briefly before it clears up and stops bothering you. However, as many as 2 out of 3 people who have episodes of acute hand eczema will go on to develop chronic hand eczema. Experts define this as eczema that lasts for three months or longer or goes away and comes back at least twice within a year.
Your doctor likely will have you undergo a patch test if your hand eczema — either irritant or allergic contact dermatitis — has become chronic.
What Does a Patch Test Involve?
Your patch test will take several days to complete. It starts with a trip to your doctor’s office. Your doctor will place three patches on your back or, in some cases, your arms. These patches contain a total of 35 allergens. You’ll then go home.
Your follow up appointment will take place two days later. In the meantime, don’t shower, sweat, or otherwise get your patches wet, as that can affect your test results.
Your doctor will remove the patches and look for signs of a reaction. You will have another appointment two days after that to check again for reactions.
It may be OK to shower between appointments — your doctor will give you instructions — but you should avoid scrubbing or scratching the skin in the test area. Other things you should and should not do during the test include:
- Don’t adjust or remove the patches without specific instructions from your doctor.
- Avoid activities that could loosen your patches or cause your skin to become sweaty. Stay out of the heat.
- Refrain from scratching or rubbing the patches or test area, even if they itch.
- Don’t use moisturizers, soaps, or other skin products on the test area.
- Keep the patches and test areas out of the sun.
- Keep the patches dry.
What Preparation Does a Patch Test Require?
Your doctor will provide you with a full list of instructions detailing what you can and can’t do in the days and weeks leading up to your patch test. Here are a few examples of what you should expect to do:
- Keep your test area out of the sun and away from tanning beds for two weeks before your test.
- Don’t use topical medications on the test area for at least a week prior to your test.
- Don’t apply moisturizers to the test area either the day before or day of your test.
- Tell your doctor if you're pregnant, as pregnancy can affect your immune system in ways that can impact your test results.
- Tell your doctor if you take any medications that affect your immune system, such as steroids like prednisone.
- Wear loose-fitting clothes to your test appointment. They should be easy to take off and put back on. Pick clothes that you don’t mind getting stained by the patch.
What Happens After Your Patch Test?
If your patch test causes a skin reaction, that means that one or more of the allergens in the test patch triggers your eczema. Avoidance of that trigger will be a key part of your treatment plan, which also may include medications to help your skin heal.
Your doctor can give you information on how to avoid the allergen(s) responsible for your hand eczema. For example, if fragrances found in certain laundry detergents are to blame, your doctor can tell you what to look for on the packaging so you know which ones to avoid and which ones to use.
Don’t give up if your test did not reveal a culprit. Your doctor can order additional patch tests — called expanded patch tests — that contain different allergens. Remember: There are lots of allergens out there. Finding yours may take time.
Unfortunately, patch tests sometimes fail to find the allergen responsible for eczema. That can be difficult, especially if your hand eczema already causes you significant stress. Being unable to pinpoint a cause can add to the emotional burden of your condition. Talk to your doctor about psychological counseling to help ease your stress.
What Are the Risks of a Patch Test?
Patch tests may cause some irritation on your skin if you have a positive result, meaning that your skin reacted to one or more of the allergens on the patch. Though quite uncommon, the tape or adhesive used to keep the patch test in place on your skin can cause a reaction. And if you have darker skin, you may notice darker or lighter skin around the spots where the patch was placed. These side effects usually clear up on their own within a few days.
In rare cases, people have had serious allergic reactions to the patch test. One such reaction, called anaphylaxis, can be life-threatening. This can happen within 30 minutes to a few hours after the placement of your patches. If you develop symptoms of anaphylaxis, call 911 and go to the nearest emergency room. These symptoms include:
- Swelling of your tongue, lips, and throat
- Shortness of breath
- Hives or a red rash
- Trouble swallowing
- Stomach pain
- Tightness in your chest
- Cramps
- Diarrhea
- Vomiting
- Wheezing
- Feelings of dread or doom
Show Sources
Photo Credit: iStock/Getty Images
SOURCES:
American Academy of Dermatology: “Patch testing can find what’s causing your rash.”
National Eczema Society: “Hand eczema.”
Cleveland Clinic: “Patch Test,” “Dyshidrotic Eczema (Dyshidrosis).”
Journal of Allergy and Clinical Immunology: “Common Contact Allergens Missed by the TRUE™ Test in an Allergy Practice.”
FDA: “Package Insert - TRUE Test.”
Tufts Medicine: “What You Should Know About Patch Testing and Contact Dermatitis.”
Lancet: “Hand eczema.”
National Eczema Association: “Skin Barrier Basics for People With Eczema,” “Understanding the Various Types of Hand Eczema.”
Mayo Clinic: “Contact dermatitis.”
Current Allergy and Asthma Reports: “Occupational Hand Dermatitis.”
Journal of Clinical Medicine: “Psychosocial Consequences of Hand Eczema—A Prospective Cross-Sectional Study.”
