STINGING TEST by HAMILTON: assessment of soothing potential of cosmetic products

23 January 2017

The notion of sensitive skin is commonly used in the context of cosmetics’ intended applications. A vital factor is the impaired epidermal barrier; therefore, what is important for the sensitive skincare regimen is cosmetic’s barrier functions, renewal, strengthening and restoring of the normal skin parameters.

Action of the cosmetics dedicated to sensitive skin also rests in the reduction of discomfort that is associated with skin tightening and burning, through the soothing effect after the application of a cosmetic product.

Sensitive skin is a condition defined as excessive reaction to environmental and chemical factors. In the pathogenesis of this condition also genetic and psychosomatic factors are considered. Clinical symptoms are defined via subjective, sensory reactions, such as, discomfort, skin tightening, stinging and burning and intolerance to cosmetic preparations. Objective symptoms are not usually observed; sometimes erythema or the flaking of epidermis might be visible. Diagnosing the appropriate parameters that characterise the dermis is not unambiguous.

There are no physical, measurable, visual manifestations that define sensitive skin. People with sensitive skin have a tendency to have less moisturised, less elastic, and more erythmatous and vascularised skin in comparison with normal population.

A subjective diagnosis of “sensitive skin” might be based on the evaluation of sensory clinical manifestations, such as pricking, burning, itching. In fact, these are clinical manifestations directly experienced by patients, but invisible for the observers. The clinical questionnaire is the best diagnostic tool in such a case. In addition to the subjective patient’s assessment, skin condition may be evaluated using a series of objective apparatus tests. Transepidermal water loss and a pH test belong to biophysical parameters that characterise skin condition.
The diagnosis of “sensitive skin” may be based on the assessment of sensory clinical symptoms (subjective).

A testing instrument is a provocation test, also known as a stinging test. The test with the use of lactic acid was first described by Frosch and Kligman in 1977. A lactic acid solution is applied to the nasolabial folds in order to identify individuals with extraordinary skin reactiveness. The application of 10% lactic acid solution to nasolabial folds on the one side, with physiological saline on the other one, allows for the comparison of presenting symptoms.

The intensity assessment is presented on the 4-point scale:
0 = none
1 = slight
2 = moderate
3 = severe

If the result is above 3 on the side where the lactic acid solution has been applied, the participant, termed as “stinger”, is qualified to the further phase of trial. The instant soothing effect is estimated on irritated skin, here one nasolabial fold is then treated with the product. A difference in stinging intensity between the side where the product has been applied and the side not treated with the product, and the soothing effect are estimated after 30 seconds, 5 and 15 minutes. For a product to be considered as soothing, there should be a profound difference between the treated and untreated zones.

The test may also be used in the evaluation of the long-term soothing effect. In such a case, the test method is based on the application of the product every day in a longer time span. If the stinging test, performed afterwards, reveals lower skin susceptibility to the irritant action of lactic acid in comparison with the initial conditions, this can be termed as a protective effect of a product.
Trials with the use of stinging test may serve as an effective tool in the assessment of sensitive skin and the soothing potential of cosmetics dedicated to sensitive skin.


Monika Makara

T: +48 58 766 99 74

M: +48 695 112 314

Chwaszczyńska, 180
81-571 Gdynia

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