- Rajani Katta MD
Allergic contact dermatitis: Why does it happen and how do you treat it?
Updated: Jan 18
I’m a dermatologist who specializes in allergic reactions of the skin. For over 20 years, I have diagnosed and treated patients with a particular type of skin allergy: allergic contact dermatitis. (hereafter referred to as ACD)
After speaking with thousands of patients about their skin allergies, there are some questions that I hear over and over again.
In this post, I want to answer some of these frequently asked questions about ACD.
Why did I develop allergic contact dermatitis, when I never had skin problems before?
That’s a great question, and it’s the million dollar question.
Why would somebody who had never had skin problems before suddenly develop an allergy to their hair dye... or to their hand cream... or even to their antibiotic ointment? The answer is that the reasons are different for every patient -- and in many cases, we just don’t have a clear answer as to why somebody would suddenly develop a skin allergy.
Sometimes it comes down to the substance itself. For example, there’s something about poison ivy that makes it far more likely to trigger allergic reactions than just about any other substance. In fact, poison ivy is so allergenic that it’s estimated that about 85% of the US population is allergic to it.
Some of it comes down to the type of exposure that you have. For example, you’re far more likely to develop an allergy to nickel if you undergo piercing with jewelry that contains nickel (nickel is a type of metal). When you get your ears pierced, those metal earrings tear through the skin barrier. Then, your skin’s immune system is exposed to a metal that it hadn’t previously seen. That can trigger an allergy.
Some of it comes down to the dose of exposure. You might be fine with using shampoo, because you’re just briefly exposed to the shampoo ingredients. If you’re using hair gel, on the other hand, you tend to have a longer exposure to those ingredients and a higher dose of exposure.
Some of it comes down to your skin barrier. If your skin barrier is impaired in any way, it means that a substance may be able to penetrate to the deeper layers of your skin. Take the example of a fragrance additive in your favorite hand lotion. Maybe your skin is extremely dry with tiny cracks because you’re overdoing it on the handwashing. If you then apply that highly fragrant hand lotion, those fragrance ingredients may be able to get through your skin barrier. Once they do that, they can reach the immune system cells that are found in the deeper layers of your skin. Those immune system cells might then jump to attention. If they think of this new substance as “dangerous”, that reaction will set off a whole cascade of events that ultimately results in the redness, flaking, and itching of ACD.
Sometimes you can have an impairment in your skin barrier that is due to genetic factors. Some people lack a certain protein in their skin barrier, and it means that their skin barrier doesn’t function as well in keeping allergens out.
There are other reasons as well that we just don’t understand yet, although research is ongoing. For example, some people seem to have immune cells that are just more quick to react and produce allergic reactions.
Is contact dermatitis due to irritation or allergy?
Contact dermatitis means that a substance contacts your skin and then causes inflammation of the skin. (Dermatitis means inflamed skin.)
Contact dermatitis can be due to irritation. For example, if you’re constantly using hand sanitizer, the alcohol in the hand sanitizer will start to strip away your natural moisturizing oils. That can cause irritation. We call that irritant contact dermatitis.
Contact dermatitis can also be due to allergy. For example, you’re out hiking and come into contact with poison ivy. Although you wash your skin a few hours later, the damage has already been done. Your immune system has already been activated. Once it’s activated, you can expect a rash, although it can take a while for the rash to show up. (Usually, you start to see the rash about 2 to 3 days later.) That’s allergic contact dermatitis.
How can you diagnose ACD?
Sometimes we can make the diagnosis based on your history.
For example, one of my friends had been coloring her hair for over 30 years. She had never had a problem. Then, one day, she colored her hair. She was just fine that day-the hair dye didn't cause any burning or other symptoms. However….three days later she woke up and her eyelids were swollen. Very swollen! Her scalp was fine, but her eyelids were red, swollen, and itchy. That history is a strong indicator that she had developed ACD to an ingredient in her hair dye.
Not every case is that clear-cut, though. In many cases we need to perform patch testing to identify the cause of ACD.
The first question we ask with ACD: what new products have you tried?
In general, if someone develops ACD, we ask about any new exposures they may have had in the past 7 days. Have you tried any new skin care products? Any new hair care products? Any new exposures at home or as a hobby? These new products or new exposures may sometimes trigger an allergic reaction.
Having said that, I see “old” products triggering allergic reactions all the time. In other words, even if you’ve been wearing the same brand of lipstick for 10 years, you can become allergic to it. (Even if the ingredients in that lipstick haven’t changed over that time.)
Why would I develop a new allergy? I used to be able to handle these products just fine.
This goes back to that million dollar question!
In some cases, we just don’t have a good explanation for why someone develops ACD. Other times, we can trace it back to certain type of exposures.
Let me give you a few examples from some of my own friends. These examples highlight several different reasons for a new allergy.
An impaired skin barrier from a chemical peel or other damage to the skin barrier. One of my friends had a chemical peel. This is a procedure that removes the top layer of the skin barrier. After the chemical peel, she started using her regular moisturizer again. Three days later, she developed an allergic reaction to her moisturizer. Our theory as to why? It likely started because she had damaged her skin barrier, and then her immune system was exposed to the ingredients in her moisturizer, and that started the allergic reaction.
An impaired skin barrier from a medical procedure. One of my patients had undergone a mole removal. She started using Neosporin to try to help heal the area. Unfortunately, two days later she developed a red itchy blistered rash in the shape of her Band-Aid (basically anywhere that her antibiotic ointment had oozed). That’s another example of an impaired skin barrier leading to ACD.
A high dose of allergen reaching the eyelids. One of my friends was working in an office, and her neighbor at the desk next to her started running an essential oil diffuser. They worked in a small office, and three days later my friend started developing red flaking rashes on her eyelids. Because she was in a small office, it’s probable that she was exposed to a higher dose of those essential oils in an enclosed space. Since the eyelids are the most sensitive skin on the body, she started to see the rash on the eyelids first.
Unknown. In other cases, I really don’t have a good explanation. Why would somebody be coloring their hair for 30 years or more…and then one day be allergic to hair dye? Hard to say, but it is possible that with all of the different chemicals that our immune system has to deal with on a daily basis, it can sometimes get “jumpier” over time.
Is blood work helpful in diagnosing ACD?
We do not use bloodwork in the diagnosis of ACD. Instead, we use patch testing, which is a procedure where we put small amounts of allergens on the back and then have you come back 72 hours later to see if you developed a rash at the area.
Although there are some blood tests in development to test for metal allergy, these are still just in development.
Can you “fix” something inside so that you don’t react to products?
Unfortunately, once you’ve developed ACD to a particular substance, we’ve never been able to find a way to reverse that allergy.
That’s different from other types of allergic reactions. For example, if you’re allergic to cats and dogs or pollen, there are ways to desensitize your immune system with allergy shots.
For ACD, we have not yet been able to develop any such technique. That’s why our focus is on avoidance: making sure that you’re not exposed to that allergen in any way.
Is there something that I can eat or something that I can change about my diet to make my skin less allergic?
That’s a really good question.
While I don’t see anything yet in the research that I believe can help us reverse skin allergies, there is intriguing research that’s suggested ways to strengthen the skin barrier.
Most of these recommendations focus on making sure you have a healthy gut microbiome. The gut microbiome refers to all of the different microbes (bacteria, fungi, yeast, others) that live in your gastrointestinal tract. These microbes play an important role in your health, because they help train your immune system and help produce certain beneficial substances. For one thing, they love fiber and can turn fiber into amazing health-promoting substances called short chain fatty acids. These substances can, in turn, strengthen the lining of your gut and also strengthen your skin barrier.
This is an article that we wrote about some of the research into diet and the skin barrier.
This is a post that goes into more detail about how a healthy gut microbiome can help strengthen your skin.
If I’m allergic to a few allergens now, do you think I’m at risk for developing more allergies?
There are certain people who seem to be at higher risk for developing skin allergies in general. And some people start out with one allergy and then develop more over time.
That was the case with me. I developed an allergic reaction to nickel after having my ears pierced as a child. (At that time they called it infected, but I suspect it was an allergy. Both infection and allergy can cause redness and blisters and oozing.)
Over the years, I have unfortunately picked up new allergies. For example, I started to react to my hair styling gel, even though I had been using it for over two years.
If I think I might be prone to allergic skin reactions, what can I do to prevent future skin allergies?
I’m prone to allergic skin reactions myself, so let me share with you what I do to prevent new reactions.
I’m extremely careful about new skin care products. Although some people can experiment with different makeup and lots of different perfumes, I take a different approach. I try to stick with a very short list of products.
The products that I choose are truly fragrance free, and don’t contain any formaldehyde or methylisothiazolinone. Here’s a list of products that I stick with myself or recommend.
When I’m using hair dye, I’m incredibly careful to make sure that none of it gets on my skin. I use a ton of pure Vaseline petroleum jelly around my hairline, on my neck, and on my ears. I want to do whatever I can to provide an extra barrier against accidentally getting that hair dye on my skin.
With perfume, I rarely use it. When I do, I try to do a small amount on the outside of my clothes.
I definitely stay away from essential oil diffusers, because I’ve seen so many reactions to those.
I also stay away from essential oils applied to my skin, because I have seen so many reactions to those.
Again, these recommendations don’t necessarily apply to everybody. But if you know that you have sensitive skin or are prone to allergic skin reactions, these measures can help you prevent the development of new skin allergies.