Skin Irritation & Anti-Irritants

By Vispi Kanga

Cosmetics and skin care products are part of most people’s daily grooming habits. Intact or uninjured skin is an excellent barrier to most substances found in cosmetics and skin care products. If skin is over dry or injured, disruptions in the stratum corneum make that barrier less protective. This is the most common cause for problems related to the use of skin care or cosmetic products, which can be simple irritation or a true allergy.

A skin irritant is any agent that is capable of producing cell damage if there is contact for sufficient time or repeated exposure and in sufficient concentrations. Even water  which is a “plasticizer” of the skin is considered a weak irritant since significant water exposure causes the loss of soluble skin’s natural moisturizing factors. The major factor responsible for irritant dermatitis and dry scaly skin is the loss of water from the stratum corneum called transepidermal water loss (TEWL).

The numerous external factors which cause TEWL include but not limited to environmental humidity, exposure to ingredients and irritants which compromises the barrier function of stratum corneum. Soaps and cleansers are considered mild irritants since their repeated and prolonged exposure results in denatured skin proteins, loss of natural moisturizing factors, disorganization or removal of protective intercellular lipids and lipid lamellar layers. There is a poor relationship between surfactant ability to remove lipid and skin irritation.
Literature has conflicting data on ability of ionics to remove lipid, while nonionics, which are
generally agreed to extract lipid are generally poorer irritants.

There is a good relationship between ability of surfactants to cause corneum swelling (protein denaturation) in vitro and their propensity to induce clinical erythema. In controlled patch tests Sodium lauryl sulfate (SLS) causes severe irritation within one day while SLES-
12 EO shows no irritation after 5 days. Corneum swelling peaks at surfactant CMC. The monomer interacts with protein. C12 alkyl chain lengths are irritating and cause most stratum corneum swelling.

The simple definition of dermatitis is inflammation of the skin. Many people think of dermatitis as synonymous with eczema but this is actually not true. It is usually used to refer to eczema which is also known as Dermatitis eczema. There are several different types. Usually all of them have in common an allergic reaction to specific allergens. The
rash of dermatitis is itchy, red, and may or may not have distinct margins. The specific look of the rash depends on the amount of time it has been present. Acute dermatitis has blisters, subacute dermatitis has scaling and crusting, and chronic dermatitis has lichenification. Irritant contact dermatitis occurs when chemicals or physical agents damage the surface of the skin faster than the skin is able to repair the damage. It depends on many factors including: Amount and strength of the irritant; time and frequency of exposure, skin susceptibility (previously damaged skin or pre-existing atopic tendency) and environmental factors.

Allergic contact dermatitis is an itchy skin condition caused by an allergic reaction to material in contact with the skin. It arises some hours after contact with the responsible material, and settles down over some days providing the skin is no longer in contact with it. Allergic contact dermatitis is also distinct from irritant contact dermatitis.

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The clinical manifestation of both irritant and allergic dermatitis are often similar – erythema
(redness), edema (swelling) and induration (hardness).

Anti-irritants refer to ingredients that can be added right into the irritating formulation, thereby making it less irritating than before. It does not refer to soothing or healing agents applied to the skin after it has been irritated. Anti-irritants seem promising in treating and preventing a variety of irritant contact dermatitis conditions, but their true effects remains under judgment. Many studies do not allow deduction of clinical effects.

Further experimentation must be performed to assess sensitivity and specificity of each anti-irritant to their specific irritant-inducing substance. Anti-irritants are usually quite specific in their activity. Some anti-irritants work via chemical reaction in mole-to-mole ratios with the irritant. Anti-irritants such as green tea and natural extracts reduce the release of cytokines and prostaglandin and protected mitochondrial enzyme.

This was proved by clinical data on the effect of green tea and natural extracts on SLS and lactic acid irritation and supported with in vitro tests. Others work via “complexation”, in which the irritant may not be exactly neutralized chemically, yet it looses its irritation potency (polyvinyl pyrrolidone). Various skin protectant ingredients are claimed to minimize irritation including dimethicone and dimethiconol. Irritation can be ameliorated by lowering the amount of the active ingredient in the formulation or by reducing the active’s penetration through the skin. Drawback of both these approaches is that efficacy is impaired.

Another classic way of diminishing irritation is by encapsulating and isolating the irritant in liposomes, microcapsules or microspheres. Many anti-irritant systems that have been identified, are based on new technologies, or simply are based on a better understanding of the interaction between the irritant and the skin and knowledge on how to modulate the irritant’s effect.

Source: SpecialChem,