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Soft and moisturized : water - what a story
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Skin properties are highly dependant of its water content. It is easy to observe that a tanned or older skin is dryer and rougher than the skin of a child. Various methods used to determine skin water content either directly or with associated characteristics such as electrical conductivity or the number of corneocytes which desquamate have now become absolutely essential.
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Dermodiag used to measure the trans epidermal water loss (TEWL)
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The corneometer
or Dermodiag operates according to the principle of electrolysis, with electrodes being applied to the skin in which the water and associated ions circulate. Current measurements indicate the amount of water present and therefore the degree of skin moisturisation.
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Measuring transepidermal water loss (TEWL) is a good indication of the skin barrier function efficiency. This is carried out using an evaporimeter, consisting of a sensor placed 3 or 6 mm above the surface of the skin. This apparatus measure the amount of water lost by evaporation. This shows that a irritant product will increase the water loss, while a moisterizer will reduce it.
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The discrimination of two small metal points, The distance of which is made smaller, until only one point can be discerned, as you reach the acuity threshold.
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The more hydrated the skin is, the softer and more supple it becomes. Consequently, it becomes more sensitive in terms of its tactile acuity, i.e. its ability to have a discriminating sense of touch. The experiment consists in the discrimination of two small metal points pushing on the subject's skin. The distance between the two points is reduced, until only one point can be discerned. This is then identified as the acuity threshold. This method enabled L'Oréal teams to demonstrate an acuity loss of 50% between the ages of 21 and 73. Il also demonstrates that applying a moisturizing cosmetic enabled some 30% to be recovered. Proving that, by improving skin surface quality, a cosmetic also improves its tactile acuity.
The sense of touch does, of course, involve neurosensory receptors. The use of micro neurography enabled L'Oréal scientists to record messages, send, by the sensors beneath the horny layer, to the brain. The more sensors there are, the more intense is their activity, the better tactile acuity will be. It might have been thought that the diminished tactile acuity of "older subjects" would be caused by "weakened" sensors. In fact, simply hydrating the skin with a cosmetic revives the connection between the sensors and the brain. Enabling the skin to "sing".
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A lipidic film resulting from the sebum secreted by the sebaceous glands, covers a normal skin. Between 1 and 5 grams a day are usually produced, anything in excess of that amount tending to make the skin shiny and oily. A simple method of measuring this secretion has been developed, known as the lipometer
or Sebutape.
A microporous film is applyied to a previously cleansed area of the skin for one hour. Sebum secretions are absoded, staining the film. The number and extent of spots have then to be quantified in order to measure sebaceous gland activity. Sebutape can characterise a oily skin and check the efficiency of a boosting lipid synthesis product for dry skin or one designed to reduce excessive secretions of sebum.
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