We frequently see ingredients labeled as irritating or comedogenic and products deemed poorly formulated, when in fact, the reasons for a reaction are often much more complex, making it especially difficult to pinpoint.
The American Academy of Dermatology reports the average adult uses at least seven different cosmetic products each day, so it should come as no surprise that in an FDA survey, up to 25 percent of people said they had a skin reaction to at least one beauty product.1 Also alarming is the estimate that over 50 percent of women categorize themselves as having sensitive skin. Some dermatologists explain this rise in skin sensitivities as a part of the “anti-aging product overload phenomenon” caused by the simple matter of probability. Macrene Alexiades-Armenakas, M.D., Ph.D., assistant clinical professor of dermatology at Yale School of Medicine, explains that “the more products you use, the greater chance one will not agree with your skin.” Too many potent anti-aging ingredients have a potential to interact with one another and cause the skin to react. Other dermatologists claim that clients mistakenly blame their skin and eye care products for irritation, when in fact, nail polish is often the real culprit, as touching or rubbing their face and eyes several times a day can trigger a reaction for people allergic to the formaldehyde and toluene in polish. Fragrances in scented hand lotions and other products can also cause similar sensitivities.

Irritant Contact Dermatitis and Allergic Contact Dermatitis
There are two types of reactions that can occur following exposure to skin care products: The first, known as irritant contact dermatitis, forms after a substance comes into contact with the skin, causing inflammation, redness, itching, swelling, burning, stinging, and occasional blistering. The time it takes for symptoms of irritant contact dermatitis to appear varies. Reaction to perfumes, for example, may occur within minutes or hours of exposure, while it may take days or weeks of continued exposure to irritants, such as soap, before symptoms begin to appear. In some cases, a person can even develop an allergic sensitivity to a product after years of use.
The other type of reaction, known as allergic contact dermatitis, involves the immune system and usually occurs in people who are allergic to a specific ingredient or ingredients in a product. Certain ingredients, such as fragrances and some preservatives, can act as antigens – substances that trigger an allergic reaction. Symptoms include redness, swelling, itching, and hives. Even though this reaction can occur on any part of the body, it happens most frequently on the face, lips, eyes, ears, and neck. Allergy symptoms may appear any time between a few hours after using the offending product and up to two weeks later. It is best to advise clients with a history of sensitivities to introduce new products slowly and to use a patch test, by applying the product to the side of the face at night in a square inch area, following up with their normal routine. If there is no sign of inflammation, such as a rash or swelling in the morning, the product is safe to use over the entire face the next night.

The Usual Suspects
The beauty products most likely to cause skin reactions include: bath soaps, detergents and cleansers, antiperspirants, eye makeup, moisturizers, shampoos, long-wearing lip stains, nail polish, and nail glue.2
Skin care products that have alpha-hydroxy acids can cause problems for some people, especially those products that have an AHA level over 10 percent. Prescription forms of retinoic acid-based wrinkle or anti-acne products can also cause irritant contact dermatitis for some, while others have reported having sensitivities to sunscreens. For these clients, almost all sun protection products can cause a dermatitis-type reaction, simply because of the way sunscreen chemicals work on the skin – a vast majority, by lowering ultraviolet radiation and releasing it as heat, which can be too hard to handle by sensitive and reactive skins. Higher silicone content in sunscreens may decrease skin sensitivity and reactivity to sun screening chemicals, being that silicones cushion and protect the skin. Even though some sources report that silicones in skin care products can cause allergic reactions or breakouts, this could not be further from the truth. Silicones are in fact some of the gentlest, safest, non pore-clogging ingredients used in skin care today. 
It is important to understand that having a negative reaction to a new skin care product does not mean the product is badly formulated. Increasing stress and environmental factors also make skin more prone to problems. Commonly used ingredients with the greatest potential for irritation are:

• Benzoyl Peroxide and Hydrogen Peroxide
• Chemical Sunscreens
• Octinoxate
• Benzophenones
• Avobenzone 
• Formaldehyde Releasing Preservatives
• Quaternium-15
• DMDM Hydantoin
• Imidazolidinyl/Diazolidinyl Urea
• Strong Sulfates: Sodium Lauryl Sulfate 
• Uncontrolled, low pH AHAs
• Propylene Glycol
• Essential Oils
• Synthetic Fragrance
• Ascorbic Acid, Retinol or Exfoliating Enzymes

Knowing which ingredients may cause a reaction is just half of the story. Many internal and external factors affecting the health of the skin’s barrier can also make the skin more susceptible to reactions, such as:

• Age
• Genetics
• Emotional stress
• Hormones
• Illness
• Disease
• Environmental stressors
• Ultraviolet exposure
• Air pollution 
• Tobacco smoke
• Cosmetics
• Microbes
• Allergens
• Topical and oral drugs
• Diet
• Alcohol
• Hot water
• Computer screens
• Smart phones

Comedogenicity and Irritation
Many misconceptions surround ingredient comedogenicity and unfortunately, skin care professionals are sometimes too quick to label an ingredient as comedogenic or the product containing it as one to avoid. Comedogenicity refers to certain ingredient’s ability to clog pores, encourage blackhead formation, or aggravate existing breakouts. In reality, only oily and acne-prone clients should be concerned about an ingredient’s comedogenic potential, as most of these ingredients simply mimic sebum’s various components.
Many lists have been circulated in our industry rating the comedogenic potential of various ingredients commonly used in skin care. These lists can be a good starting point for weeding out highly comedogenic materials from products intended to be used on oily and acne-prone skin, but when considering a product’s possible comedogenicity, the following factors need to be taken into account:

1. Quantity of the ingredient used in the product.
2. Presence of other comedogenic ingredients.
3. Length of time the product remains on the skin.
4. Where the product is used on the body.

Are Hypoallergenic Products Safer?
Despite countless rows of products on the market touting “hypoallergenic” claims and an implied notion that they are less likely to cause reactions, it is important to understand that some of these products may not necessarily be gentler or even safer for the skin than other products. The FDA admits to having no federal standards or regulations governing the use of the term hypoallergenic, which means that the decision as to whether or not a cosmetic may be labeled as hypoallergenic lies solely with the manufacturer. The term hypoallergenic may be applied without any demonstration or proof that the product causes fewer allergic reactions than others.3
There are numerous factors that send our complexions into a tailspin. Sometimes formulations are to blame, while other times problems occur due to a personal reaction to an ingredient or a combination of ingredients. It is important to acknowledge that reactions to skin care products are complex and it is best not to make a habit of hastily identifying the culprit without taking all factors into consideration. It may very well be that their cleanser is just too harsh or stripping or that they are using the wrong product for their skin type, but it may also be that their skin is simply more reactive and exhibits sensitivity to skin care products in general, regardless of the ingredients. 
References:
Barrett-Hill, Florence, (2001). Comedogenic Effects of Cosmetic Raw Materials. WebMD, Cleveland Clinic. Web.

1 Girdwain, Jessica, (2011). What Type Of Sensitive Skin Are You? Prevention. Web.
2 Chularojanamontri Leena, M.D., et al., (2014). Moisturizers for Acne What are their Constituents? The Journal of Clinical and Aesthetic Dermotology. Web.
3 Stoppler, Melissa Conrad, M.D., et al., (2008). Are Hypoallergenic Cosmetics Really Better? Medicine Net. Web.

Irena James, director of product development for YG Laboratories, has educated generations of students and industry peers on skin care ingredients, treatment protocols and brand development. Irena’s versatile experience in the skin care industry spans over 20 years, during which Irena worked as an aesthetician, educator, territory sales manager and director of business development in the EU. She is an assistant instructor at the UCLA Extension Cosmetic Sciences Program and a member of BIW and the Society of
Cosmetic Chemists.