Inflammation, irritation and allergy are medical terms. They are sometimes used in inappropriate ways and are sometimes used while exchanging one for the other. Inflammation is a symptom. It is the symptom that something unwanted is occurring to our skin and that the skin is reacting. Inflammation is defined as the presence of redness, swelling, heat and pain. When one of these four aspects is missing, we do not speak of inflammation. Inflammation can be the consequence of aggressions as diverse as bacterial infections or traumatisms. The inflammatory response is mediated by the immune system. Three main processes occur at the onset of inflammation: the capillary vessels enlarge when supplying blood to the damaged region, resulting in increased blood flow and therefore redness (erythema) and heat. The capillaries become permeable to cells and fluids and the releasing of fluids causes swelling (edema). The blood vessels release neutrophils, white blood cell containing enzymes that digest microorganisms and can also damage the tissue, thus causing pain. The inflammatory response is a beneficial response: infections, wounds and any damage to tissue could not heal without an inflammatory response.

Irritation is a symptom, too. It is the symptom that something unwanted is occurring to our skin and that the skin is reacting. Irritation is defined as the presence of redness and pain, and can be provoked by aggressions as diverse as treating the skin for a few minutes with a solution containing 1% to 2% of sodium lauryl sulfate or simply scratching the skin itself. Some medical dictionaries state that irritation is not mediated by the immune system.

Redness in inflammation or irritation is the consequence of vasodilation, the enlargement of the sub-epidermal blood vessels. Redness itself can be provoked by vaso-dilating agents such as niacin or methyl-nicotinate.

Allergy

Allergy is not a symptom. Allergy is a phenomenon that provokes symptoms such as irritation or inflammation, and sometimes also anaphylactic reactions. In general, when skin is treated with 5% SLS, everyone develops an irritation. In the presence of bacterial infections, everybody develops an inflammation, too. On the other hand, only a few individuals develop an irritation when put in contact with nickel, or when eating peaches or strawberries. In these cases we speak of “allergy.”

The term “allergy” was coined by Clemens von Pirquet in 1906 to call attention to the unusual propensity of some individuals to develop signs and symptoms of reactivity, or “hypersensitivity reactions,” when exposed to certain substances. The word allergy is created from the Greek words “allos” (foreign )and “ergos” (work), to mean the “action by a foreign body.”

Allergy is a phenomenon that concerns a minority of individuals. When people who have never been in contact with, let’s say, strawberries, come in contact with this fruit, nothing visible will appear. The second time they come in contact with strawberries, in a minority of those persons something visible such as a rash can happen. Since the vast majority of the persons do not develop a rash when they eat strawberries, we say that the reacting minority is made of persons who are allergic to strawberries.

During the first contact, a process called “sensitization” is triggered. In this process the immune system of the individual allergic to strawberries recognizes “something” as foreign and unfriendly. Upon the second contact, the immune system of the person allergic to strawberries is ready to fight the foreign and unfriendly “something” and triggers a reaction characterized by irritation or inflammation.

In a few dramatic instances, an allergic reaction provokes an anaphylactic shock, from the Greek meaning “excess protection.” Anaphylaxis causes the immune system to release a flood of chemicals that can make somebody to go into shock— the blood pressure drops suddenly and the airways narrow, blocking breathing. Signs and symptoms include a rapid, weak pulse; a skin rash; and nausea and vomiting.

Allergy in Skin Care

In the skin care industry, many ingredients are known to provoke allergic reactions; for instance, nearly 1% of the population is allergic to rosemary extracts. The industry therefore tends to avoid using ingredients known to provoke allergies. The fact is that new ingredients are continuously generated, particularly botanical extracts that may provoke allergies (these materials are said to be allergizing). The majority of allergenes (the materials that provoke allergies) are found in fragrances, and it is therefore a good policy to prepare fragrance-free products. Since allergenes can be found everywhere, it is a good policy to test new raw materials and finite products in an allergy test. One such test is the 30-day Human Repetitive Insult Patch Test (HRIPT) which reproduces in a clinical laboratory, the conditions of sensitization and of the allergic reaction.

This test consists of applying under a patch, on the skin of human volunteers, samples containing different dilutions of the product to be tested, and re-applying every second day for two weeks (this is Phase I or sensitization phase). After a two-week rest period, the product is applied again once (or twice at 48 hours interval) (this is Phase II or elicitation phase). When no erythema develops, it is said that the volunteer is not allergic to that product. Obviously it is necessary to test the product on large groups of volunteers (from a minimum of 50 to an unlimited maximum) and the fraction of volunteers in the group reacting to the products gives an indication of the acceptability of the product in the market. If the cohort of volunteers is composed of 50 panelists and three of them develop a rash, the executives of the brand must ask themselves whether the market can accept 6% of adverse reactions or whether such a result might create a bad image for the brand.

A product that is “negative” in an HRIPT test, that is, a product that does not elicit a rash in the cohort of volunteers, is said to be “allergy tested.”

One could even push the claim a little further by stating that the product is “non-allergizing”... (for the panelists in the cohort, of course).

On the other hand, it is difficult to understand what is meant by the term “hypoallergenic”—a juxtaposition of the Greek words “hypo” (which means under or below), “allos” (which means foreign or different) and “genos” (which means generate or produce).

With a lot of imagination, one could understand hypoallergenic as meaning ”below the generation of difference” which is meaningless. For sure it is a successful word insofar as, without using medical terms, it evokes an action against allergy. It also frustrates all attempt to prove false the statement, “this product is hypoallergenic,” because such a statement does not mean anything and therefore it is neither true nor false.

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Paolo Giacomoni, PhD
Insight Analysis Consulting
paologiac@gmail.com
516-769-6904

Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as executive director of research at Estée Lauder and was head of the department of biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents.