Water is a vital chemical that hydrates and ensures correct functioning of our skin. Our body contains approx. 70% water which helps keep the outermost layer of the skin (the Stratum Corneum or SC) flexible.Devoid of water it becomes hard and frail susceptible to cracking and splitting. Hydration also regulates biochemical processes going on within the skin which control its growth, and eventually how the outermost cells are lost.This article will help you explore:

• Methods to Measure Hydration in the Stratum Corneum
• Protocol to Evaluate the Efficiency of a Moisturizer
• Watchouts When Measuring Skin Hydration

Methods to Measure Hydration in the Stratum Corneum

A number of methods exist to measure hydration within the stratum corneum. Most rely on changes in the electrical properties of the skin as a consequence its degree of hydration – dry skin has very different electrical properties to hydrated skin. Techniques such as the Corneometer look at these electrical properties and use them to deduce the skin’s hydration status.

As with most skin methods, no two devices are ever precisely the same in how they measure the water, and as such it is good practice to use the same device throughout a study, and to always do change from the original condition, and also to measure untreated sites of skin, to determine whether there has been any day to day change in the skin itself.

Skin hydration measures are used for measuring the efficacy of moisturizers, and also for testing the drying effects of cleansers.

Protocol to Evaluate the Efficiency of a Moisturizer

With moisturizer testing an area on the skin is marked out, and the baseline hydration state measured. A standard amount of moisturizer is applied to the skin in the marked out area (typically 2μl cm-2), applied in a controlled way using a gloved finger and allowed to dry. As most moisturizers contain water, if the area where the product has been applied is measured too quickly, the water in the product itself is detected, giving a false reading of the skins hydration.

It is recommended that at least 30 minutes is left between applying the product and the first reading to give the water from the product time to evaporate. The site can then be measured over time to see how the skins hydration level changes after product application. These types of tests are used to develop “hydrates your skin for 24 hours”, or “more hydrating than leading competitor” types of claims.

When looking at cleansers and how they can dry the skin, typically longer studies are done (up to 2 weeks) with regular product usage, and the hydration state of the skin measured at the beginning and end of the study.

Watchouts When Measuring Skin Hydration

There are watchouts when measuring skin hydration. As well as the issues with moisturizers as discussed above, the devices are sensitive to how they are placed in contact with the skin, so the operator needs to be well trained, and familiar with the device being used. As they rely on contact with the skin, the presence of hair will prevent good contact and cause them to give low readings. Too much pressure when holding the probe on the skin should be avoided as this artificially raises the values measured. As with all skin measures, the panelist need to be acclimatized in the room where the measurements are done so that they become used to the temperature. Standard conditions for skin measurement are 20-21°C and 50% humidity – if the temperature or humidity are significantly higher than this then the panelists begin to sweat which obviously has a huge impact on measures of hydration.