Allergen, Not An Allergen, Featured, Skin

It’s Complicated: Allergic Versus Irritant ReactionFeatured

It's Complicated: Allergic Versus Irritant Reaction

A reaction is a reaction…isn’t it?

Yes, in that a skin reaction usually looks and feels “off.” No, in that a skin reaction can be irritant or allergic. Some substances can be irritants but not allergens (such as the iodine on the bottom right of the photo above) or allergens but not irritants (such as the lemongrass essential oil on the top left of the photo above). Always trust your dermatologist to make the diagnosis, but this is a quick overview to help you understand the difference between the two:


An irritant reaction is a form of contact dermatitis but it is not an allergic response. According to DermNet NZ, “Irritant contact dermatitis is a form of contact dermatitis, in which the skin is injured by friction, environmental factors such as cold, over-exposure to water, or chemicals such as acids, alkalis, detergents and solvents.”
Irritant reactions have a relationship with the concentration of the ingredient in a product, the frequency of your skin’s exposure it, and how long your skin is exposed to it. While a diagnosis needs to be made by your dermatologist, here are examples of what an irritant reaction might look like:

  • You use a moisturizer most of your life and experience relatively mild symptoms like dryness that you don’t think of as a reaction, but that are, in fact, mild irritant reactions. If you spread on more of the moisturizer or use it more often, you notice more dryness or possibly other symptoms like redness. If you stop using it for a while, the symptoms subside. And when you use it again, you don’t notice a problem unless you use more of it or use it more frequently.
  • Babies often get an irritant reaction from their saliva around the mouth and on the chin. The reaction goes away as they drool less as they get older.
  • Temporary burns from strong chemicals like chlorine.
  • Itching and redness after touching certain insects.
  • Dry, red, itchy skin from winter or dry, cold air.
  • An instant redness or itching after applying a certain threshold amount of a cosmetic product (in an allergic reaction, the symptoms would appear regardless of the amount applied).


An allergic reaction is a true allergy, meaning that the body has an immune response to an allergen.
You can use something for weeks, months, or years without a problem and then only later develop an allergy to it. This happens once your cells recognize a substance as foreign. After this, on repeat exposure, the allergic reaction occurs even with exposure to small amounts of the allergen (whereas an irritant reaction would require a certain threshold amount to elicit a reaction). If you are allergic to a substance or develop an allergy to it, any percentage of it for any amount of time on the skin will cause a reaction.

Irritant Versus Allergic

The percentage of an irritant or allergen (how much of it was applied or how much of it the skin was exposed to) is important in differentiating irritant and allergic contact dermatitis.
Irritants at a high concentration cause acute irritant contact dermatitis (marked swelling and blistering), such as after just a one-time exposure to a strong acid. At lower concentrations of an irritant and/or constant exposure to it, a chronic irritant contact dermatitis can develop. You might see this in the hands — the skin becomes thick and leathery — of people who work in the health, laundry, or cleaning industries from the frequent exposure to strong soaps and cleaning agents. That said, you could also actually build a tolerance to mild irritants over time.
In allergic contact dermatitis, you may be exposed to an allergen for weeks, or even most of your life, and not react to it. This changes once your skin’s T cells recognize the allergen as “foreign” or “bad,” and develop an immune response then a delayed response that continues every time you are exposed to it from that moment on. Once this immune response is set, any amount of the allergen shortly after contact with your skin will cause a reaction.
An allergic reaction can coexist with an irritant reaction. For example, dryness or redness from the frequent use of alcohol, bleaches, chlorine or other disinfecting products could be an irritant reaction. But if the products also contain fragrances, preservatives, formaldehyde or other top allergens, you might also develop an allergic reaction.
Contact dermatitis experts are the specialists to accurately identify whether the skin changes you are seeing — dryness, redness, dark patches, and other symptoms — are an irritant or allergic reaction. A patch test is important to accurately identify which substance or ingredient is causing the reaction, and patch tests can also confirm if a reaction is allergic or irritant. After you get your patch test results, you’ll know exactly what you need to avoid. And often, just simple and careful avoidance of the substance can give you relief and clarity.


Check out the other posts related to contact dermatitis:

Allergen-Not An Allergen
Get A Patch Test Or Photo-Patch Test
On Contact Dermatitis, Sensitive Skin, and Patch Testing: Interview with an Expert

Laura is our “dew”-good CEO at VMV Hypoallergenics and eldest daughter of VMV’s founding dermatologist-dermatopathologist. She has two children, Madison and Gavin, and works at VMV with her sister CC and husband Juan Pablo (Madison and Gavin frequently volunteer their “usage testing” services). In addition to saving the world’s skin, Laura is passionate about health, inclusion, cultural theory, human rights, happiness, and spreading goodness (like a great cream!)


On Contact Dermatitis, Sensitive Skin, and Patch Testing: Interview with an ExpertFeatured

Is a rash a skin allergy or an irritation? What is a patch test and why would I need one? How can I prevent rashes? To get clarity, we spoke to Jenny Murase, Chair of the CAMP Optimization Task Force of the American Contact Dermatitis Society, Associate Clinical Professor at UCSF, and Director of the Patch Test Clinic at the Palo Alto Foundation Medical Group.

1) We understand that the American Contact Dermatitis Society is an organization for dermatologists who are interested in or specialize in contact dermatitis. Why is the ACDS necessary?

The ACDS provides a critical role in the dermatology and allergy community. Our society is a group of subspecialists who provide diagnostic testing for dermatitis (rash). When someone gets a rash that is chronic (lasts a long time) and recalcitrant (does not respond to therapy), it is possible that there is an external component to consider. Irritant contact dermatitis and allergic contact dermatitis are both possible. Through our patch testing, we help to uncover what could be triggers for rash. The ACDS provides dermatologists and allergists with tools to educate their patients during this testing, such as handouts describing the patient’s allergens and the Contact Allergen Management Program (CAMP) which creates a safe list of products for patients that do not contain their allergens.

2) What are some common allergens?

These include some substances in skin care products like some preservatives, fragrances, surfactants, and emulsifiers as well as hair dyes, textile dyes, metals, topical medications like antibiotic ointments or topical steroid ointments, plastics, rubbers, adhesives, among many other allergens.

3) What is a patch test and why is it useful?

Patch testing is a diagnostic test that looks for delayed hypersensitivity reactions, which means rashes on the skin that develop in response to an allergen coming in contact with the skin that the patient has developed memory immune cells to recognize and respond to. A classic example would be poison oak, where a patient is exposed and then develops a red rash within days because they have immune cells that respond to the poison oak allergen. This is different from an immediate hypersensitivity reaction mediated by histamine which results in an immediate reaction on the skin, like contact hives (urticaria) or an anaphylaxis reaction (like latex allergy, for example). Because this is a delayed reaction, it takes a few days to read the test. Patches with certain substances are placed on the back and are removed after 48 hours, with an interpretation at 3-7 days after placement to see how the patient is responding to the allergens.

4) What are some of the causes of skin allergies and what are some best practices to manage them?

I listed the causes of skin allergies in my answer for question two, and the best practice is avoidance of the allergen, if at all possible. We provide patients with a safe product list through CAMP for skin care products ranging from shampoos, soaps, moisturizers, and even laundry soap and detergents. We also provide ways to avoid non-skin care product allergens like rubber in certain rubber gloves or textile dye allergy through dye-free clothing. In addition, we provide dietary tips on how to avoid consuming some allergens that can cause a “systemic contact dermatitis,” including allergens like tocopherol, propylene glycol, balsam of peru, cobalt and nickel.

5) Is sensitive skin common or is it all hype/a trendy excuse?

Sensitive skin can mean a variety of things to patients. Someone who has had hives (urticaria) or eczema (atopic dermatitis) can feel that they have sensitive skin since their skin breaks out in rashes easily. It can also mean that they have become more and more sensitive to skin care products throughout their life by developing allergic contact dermatitis slowly over time. Diagnostic testing like patch testing can help to clarify what is driving the rash and/or the itch.

6) What is CAMP, why was it created, and how does it help patients who’ve had a patch test?

CAMP is the Contact Allergen Management Program. It was created for ACDS members in order to be able to provide a safe list of products that do not contain the allergens that the patient is allergic to or any of the cross reactants. It can be difficult to read labels if you do not know all the different chemical names and cross reactors. For example, if you tested positive to formaldehyde, you needs to avoid ingredients like Quaternium 15 and DMDM Hydantoin. CAMP takes the guess work out of finding safe products for the patient because it is easier for them to look for items on their safe list and buy those than to try to process all the possible reactions.

7) We heard there’s a new app for CAMP! Is it for me (does my dermatologist have to be a member of the ACDS), and how can I check?

In order to get access to the CAMP app, your dermatologist needs to be a member of the ACDS. CAMP will generate codes that you place into the app when it is downloaded to the phone, and using these codes, a list of products that do not contain your allergens can be generated.
Find an ACDS-member provider in your area that does patch test on the ACDS website.
We publish articles by doctors who wish to provide helpful information to their patients and the public, or who respond to our requests to use them as professional resources. Doctors may or may not prefer to remain anonymous and we respect this preference. These resource articles do not in any way imply an endorsement by the physician of VMVinSKIN.com or VMV HYPOALLERGENICS® — they are intended for informational purposes only. While written by or with resource professionals, these articles should not be relied on for diagnostic accuracy or applicability to your particular skin, which requires an in-person ocular consultation with a qualified physician and possibly additional diagnostic tests.