How to Tell the Difference Between Nummular Eczema and Ringworm
It’s often difficult to distinguish between nummular eczema and ringworm, so it’s always best to be evaluated by a dermatologist, say experts.
Published On: Aug 7, 2016
Last Updated On: Jul 15, 2021
Atopic dermatitis is often the beginning of the atopic march: babies start out with eczema and perhaps food allergies. Later on, asthma develops, possibly along with inhalant allergies, or allergic rhinitis and hay fever. During this time the body’s allergic antibodies, the IgE, increase in the blood.
One of the questions is: Why do people get eczema and allergies? This has prompted a chicken-or-the-egg debate. Do we begin with a skin problem due to a defective skin barrier, which allows allergies to get into the body and cause immune dysregulation? Or does it start with an allergic immune system, which leads to inflammation and renders the skin barrier defective, causing eczema in a vicious cycle?
Over the past several years, we’ve seen a lot more evidence to indicate that there is an intrinsic skin defect, which allows allergens to enter through the skin. The immune cells in the skin prompt a variety of other cells to form, which cause allergy. Perhaps if more exposure occurred through the gut, we might have a better shot at correcting the immune system, and allowing patients to develop a tolerance.
This idea, however, is oversimplified, and differs for individual patients depending on their genetics. The most commonly reported skin barrier protein defect is a filaggrin gene mutation and this increases the risk of eczema. This skin barrier defect allows allergens to enter through the skin. A number of excellent genetic studies have shown that if this skin barrier protein defect is present, there also exists a greater risk of developing peanut allergy and atopic dermatitis.
The interaction of environment and genetics can also play a part. For example, an infant with a filaggrin defect living with a cat in the home has increased risk of developing atopic dermatitis and asthma. Other studies have shown that people with atopic dermatitis with a filaggrin defect also have an increased risk of pollen allergies.
However, when we think about atopic dermatitis, allergens are just one of the triggers, along with dry skin, irritants, anxiety, and stress. As an allergist who has a passion for atopic dermatitis, I often see families come in and say to me, “Tell me what food is causing this eczema.” And I have to say, “Well, there are a lot of things going on here, we have to think about the skin barrier and sort of step back from this.”
Many times, eczema flares can be erroneously attributed to foods; a lot of times these flares can be precipitated by other things such as irritants, detergents, humidity, changes in temperature, stress, and infection.
That brings us back to skin care because it is of critical importance. Several years ago, Dr. Jon Hanifin and his team at Oregon Health & Science University did a nice study, which showed that after eczema patients with allergy concerns learned and practiced good skin care, their allergy concerns were lessened.
We want to do a good job caring for the skin because we know that it can provide a protective barrier. Because we know that allergens can enter through the skin, we’re concerned that by not protecting the skin barrier, patients can end up sensitized to the allergen.
I lead a team at the Boston Children’s Hospital Atopic Dermatitis (AD) Center. Several years ago, one of our fellows completed a review of all AD Center patients in order to see what helped them most.
We found that the factor that correlated most with an improvement in atopic dermatitis was not whether the patient eliminated a food from his or her diet or whether he or she engaged in environmental control; it was whether improved adherence to the treatment regimen was possible.
If we could give the patient (in this case it was parents caring for pediatric patients) a treatment regimen that they could follow and that de-creased their concern of treatment side effects, we found that this correlated with patients getting better.
We know food allergy and atopic dermatitis are highly associated. While not all atopic dermatitis patients have food allergy, up to 20 to 40 percent of children with moderate to severe atopic dermatitis will have an IgE-mediated food allergy. Which brings us to the controversial question: Can food allergies exacerbate atopic dermatitis?
We know that the two coexist, but we don’t know whether food allergies make atopic dermatitis worse. There are some studies that suggest that patients with positive allergy testing to egg may get better if they eliminate eggs from their diet. This creates some cause for concern because taking the allergen out of a diet may prevent patients from developing an oral tolerance. We do try to be very careful with diagnosing food allergies.
A few years ago, I had the pleasure of participating on an expert panel that developed guidelines for food allergies. One of the most difficult guidelines to develop was the question of food allergies in atopic dermatitis.
I think the panel came to the conclusion based on the evidence and expertise that we had: The guidelines say that children less than 5 years old with moderate to severe atopic dermatitis may be considered for food allergy evaluation for milk, egg, peanut, wheat, and soy, if at least one of the following conditions is met:
It’s best to take care of the skin first, and then look for food allergies. In my experience, and that of our allergy group and dermatology group at Boston Children’s Hospital, when we see infants, who have weeping, unrelenting facial involvement and severe AD starting at a young age, and who don’t improve with optimized skin care, then we find that looking for food allergies can be beneficial.
How do we look and test for food allergies? Through skin testing and blood testing which looks at the specific IgE for the allergen. Skin tests are beneficial in that they have greater accuracy and are available for many different allergens. They are also less expensive and deliver same-day results. However, to undergo skin tests, patients have to stop antihistamines.
Blood testing is a little more convenient; they have a more quantitative result, and they are not affected by anti-histamines. Blood tests are particularly preferable to skin testing if the patient is very young or uncooperative, has had anaphylaxis to a food, or has extensive eczema and there’s not a good place on the skin to test.
A negative result indicates that allergy is very unlikely to be the problem. A positive test means that the allergic antibody is present.
However, a positive result doesn’t necessarily mean that you’ll have an allergic reaction, because there’s a very high false positive rate (as high as 50 percent) with test results, which means that even though the test is positive, the patient might actually be able to ingest the food without difficulty.
This is why performing random screening in atopic dermatitis patients isn’t particularly helpful, because you’ll find positive testing for foods that patients could actually eat. At this point, we need better diagnostic testing to figure out what’s true allergy and what’s not.
Currently, there’s a peanut component test in which we look at the specific IgE to individual peanut proteins. Specific IgE to one component Ara h 2, is more associated with having peanut allergy than some of the other proteins. Patients can sometimes test positive for a general peanut specific IgE, but when you look at the components, you’ll find that they’re positive to the components that cross-react with pollens and other plants and negative to Ara h2. In this case the patient would likely tolerate peanut.
The most common food allergies in patients with atopic dermatitis are milk, egg, and peanuts. There are a number of uncommon allergens, like chocolate. Corn is also less likely to cause allergies. While citrus fruits, berries, and tomatoes are unlikely to cause actual allergic antibody (IgE)-mediated reactions, they may cause facial irritation.
Many babies will get red faces when they have tomato sauce and that’s okay. It doesn’t mean they’re allergic, it’s just natural chemicals in those foods that cause an irritant reaction.
Until we have better testing, the most reliable way to know whether a food allergy exists is to perform a food challenge, which should be done under medical supervision.
When it comes to allergies in the air, inhalant allergens and atopic dermatitis are highly associated and often occur together.
Common allergies include pollen, dust mites, dogs, and cats. To diagnose inhalant allergies, we look for a history of itching, sneezing, wheezing, and coughing in a patient with exposure to the allergen. The same kind of allergy skin testing or blood testing is done for inhalant allergies. There are fewer false positives with inhalant testing than with food testing.
There’s not a lot of work on this but there have been a couple studies. In one interesting study done 20 years ago (which I think would be hard to do today), researchers looked at an aeroallergen bronchial challenge. Researchers took 20 atopic dermatitis patients who had a positive skin test to dust mites and gave them small amounts of dust mite by inhalation. They found that nine of the patients had skin symptoms after they had inhaled the dust mites, primarily in the places on the body where they usually got their eczema. All of these patients also had decreased lung function.
Recently, there’s been more work using allergy shots, also known as immunotherapy. Some data indicates that allergy shots can be effective for atopic dermatitis when associated with inhalant allergies. Additionally, in the review of four placebo controls (in which there was an active arm and an inactive arm), there was significant improvement in atopic dermatitis symptoms for patients who received allergy shots for dust mites.
As of now, there aren’t any good studies, which show the correlation between dust mite control and lessening atopic dermatitis. However, because most dust mite control measures are relatively easy to do, we tend to recommend them.
Dust mites love humidity, heat, clutter, and skin scale, (which frequently occurs with patients with atopic dermatitis).
To help control dust mites, try the following:
To limit exposure to pollens, use air conditioning. This can also help ease sweating and further itching. Showering or bathing and washing your hair in the evening can also help. Finally, keep outdoor equipment and clothes outside of the bedroom, so you’re not bringing the pollen in with you.
If you have severe allergy symptoms to animals, it’s best to find the pet a new home. Otherwise, minimize exposure by keeping the animal in certain areas and out of the bedroom, clean frequently, or run a HEPA filter.
There are not a lot of studies on molds and atopic dermatitis, but I have found molds to be a trigger for selected patients.
Keep humidity less than 40 to 50 percent and clean areas that are prone to mold growth, using dilute white vinegar or dilute bleach to control mold. If you have any areas affected by water damage, you’ll likely need to hire a professional to get the space repaired.
With contact dermatitis, the most important thing is recognizing history and the location of the rash. Contact dermatitis experts say: “location, location, location.” As in, where is the skin affected?
A contact dermatitis rash may look similar to an atopic dermatitis rash. However, it may look a little different in that it may feature vesicles and blisters.
Patch testing should be done in order to identify contact allergens. I recommend seeing a contact dermatitis expert because patch testing can be tricky.
Patients who undergo testing have patches placed on their skin for 48 hours. About 72 to 96 hours later, some of the allergens are read. Other allergens won’t display for up to 5 or 7 days later.
There a lot of substances that cause allergic contact dermatitis, such as poison ivy and other plants, fragrances, hair dyes, adhesives, and even some topical medications made with preservatives.
A common allergy is nickel contact dermatitis. I’ve seen patients with nickel dermatitis on the bridge of the nose from reading glasses, the neck and ears from jewelry, and near the belly button from the snaps of jeans. Fabric dyes and finishes can also pose a problem.
To treat contact dermatitis, identify and remove the allergen, then use topical steroids (or rarely an oral steroid in severe acute cases). If small items like metal snaps are causing irritation, you can use an alternative metal or apply a coat of clear nail polish or some duct tape onto the item in order to help.
Lynda Sch
neider, M.D., is an Associate Professor of Pediatrics at Harvard Medical School and Director of the Allergy Program, Division of Immunology Clinical Research Program, and the Atopic Dermatitis Center at Boston Children’s Hospital.
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