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Firm and supple
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The way in which skin reacts to the mechanical constraints of pinching, twisting, pulling and creasing vary from one person to another. The methods used will attempt to measure the degree of deformation and the time required for the skin to return to its original state.
The skin's firmness and elasticity reflect the elastic properties of the connective tissue in the dermis and the overlapping of collagen and elastin fibres. Over time, this network becomes disorganised, causing this firmness and suppleness to decline.
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Resistance to torsion quantified by Torquemeter
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As its name implies, this device measures a material's resistance to torsion. For use on skin, researchers have adapted the technique of the torquemeter
to limit the area subject to the stress - and produced the twistometer ! This device is now sold and regularly used to assess a cream's effectiveness on the skin's visco-elastic behaviour (elasticity and firmness).
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Cutaneous creasing quantified by Densi-score.
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This device works on the principle of correlating "skin density" with skin creasing. A baby's skin does not show any creases when pressed between two fingers, whereas that of an older subject will show multiple. This is because a baby's skin has a higher density.
The Densi-score
device, patented by L'Oréal, is based on this observation and consists of applying a reproducible mechanical creasing force of 40% on the forearm. The calibration enables the number of creases to be correlated with the skin's density. This diminishes with age due to the destructuring which takes place in the dermis and rigidification of the horny layer, resulting in creases becoming more frequent.
Scales of creasing are therefore drawn up according to density and age. These are then used to assess the efficiency of an anti-age product designed to improve skin firmness.
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This portable device, consists of two plates applied to the surface of the skin, and is used to measure the mechanical characteristics of the cutaneous envelope. Initially, the plates are set 10 mm from each other and are then drawn apart by a small motor, stretching the skin by about 30%. A force sensor plots force-extension and force-time graphs once the motor has been stopped. The degree to which the skin can be extended reflects its suppleness.
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