Qualifying cleansers

A new technical skin model will help simplify the development of cosmetic products, says Claudia Balluff

HUMskin is the name of a standardised technical skin model that should greatly simplify the development of cosmetic products in the next few years. HUMskin is based on a modified biopolymer and simulates the physiological, mechanical and topographic properties of healthy human skin. For example, the surface of the technical skin substitute material has a typical field structure and its pH value is similar to that of our skin, pH5.5 – slightly acidic. The physiological parameters of HUMskin, such as moisture content and transepidermal water loss (TEWL), have also been made to match the known values for human skin.

The technical skin model, the name of which comes from the words ‘human’ and ‘skin’, was developed by the Hohenstein Institute in Bönnigheim, Germany. There, Professor Dirk Höfer and his team have, over recent months, used HUMskin and a specially set up trial to compare the effectiveness of various different cosmetic cleansing products. Now that the technical skin model has proved its suitability for large-scale tests, the scientists are able to offer standardised testing for cosmetics manufacturers.

For the first time, HUMskin will enable them to have objective and reproducible tests carried out on raw materials and products. These tests are also particularly efficient and cost-effective because they do not require human volunteers.

Comparing performance

It is only possible to test the effectiveness of cleansing wipes, facial toner and special make-up removers objectively in the laboratory or in field trials with volunteers to a limited extent, because of the many external factors that can influence the tests. Such trials are also extremely time-consuming and expensive.

By using HUMskin to carry out ex vivo tests, on the other hand, all external influences can be completely excluded.

The test conditions are standardised so that the results can be reproduced at any time.

For example, to compare the cleansing performance of make-up removers using HUMskin, the research team first applies a defined quantity of slightly radioactively marked make-up particles to it. With the help of a special rubbing device, the make-up particles are subsequently removed again using different cleansing products in standardised conditions. Then the amount of radioactive make-up particles that remain is measured using a scintillation detector, a special radiation measuring device, thereby providing an objective assessment of the cleansing performance. In some cases, this varied greatly between the products being tested: for example, a liquid eye make-up remover performed approximately 70% better when removing water-resistant eyeshadow than a wipe soaked in a lotion.

Measurable differences

These tests developed by the Hohenstein researchers mean that HUMskin can be used to demonstrate significant differences in cleansing performance for the first time. Compared with this, the results of laboratory testing and field trials using volunteers have always been rather unsophisticated. For example, in 2007, the volunteers for the consumer magazine test assessed the cleansing performance of all the 13 eye make-up removers that they tested as good. The assessments varied between 1.6 and 2.1, ie in a very narrow range. Even this critical assessment by the volunteers was affected by their personal preferences for factors such as the consistency and the aroma. If you compare the cost of trials using volunteers and the actual value of the results, the outcome is often quite disappointing.

Synthetic skin model HUMskin simulates the physiological, mechanical and topographic properties of human skin; it can be used to demonstrate differences in cleansing performance

That is why quick and realistic tests using the technical skin model offer an interesting alternative for use in product development and open up new testing options for cosmetics manufacturers.

By using HUMskin, they will be able to measure and evaluate differences in cleansing performance far more accurately in future. This highly differentiated data is important if premium-quality cosmetics that already perform to a high standard are to be improved still further and the differences in quality made clear to consumers, objectively and plainly.

Better make-up removal

This is particularly important for facial cleansing products. Thorough cleansing to remove make-up particles, eyeshadow, rouge, perspiration, sebum and dead skin cells completely from the skin is the basis of all effective skin care. If you wear make-up, you should therefore remove it from your face every day using special cleansing products. Any traces of make-up that remain on your skin form an insulating layer that is not healthy. It makes it hard for the skin to breathe and blocks the pores. The night-time regeneration process is disturbed; this results in reddening and spots, and a sallow appearance. Eyelashes from which the mascara is not removed will break off. Traces of kohl irritate the sensitive conjunctiva and can cause styes and inflammation, which are often painful and require medical treatment.

Radioactive particles of make-­up are applied to HUMskin – Hohenstein experts then calculate how many particles remain after rubbing

The quality of the cleansing products is particularly important when removing eye make-up, because the skin around the eye is 0.5mm thinner than the skin on the rest of the face and there are also fewer sebaceous glands there to keep the skin moist. Therefore, cleansing needs to be especially gentle when removing eye make-up. A good cleansing product will remove all traces of make-up completely without damaging the sensitive skin around the eyes.

Perfect simulation

As well as measuring the cleansing effect, the technical skin model can also be used for testing many products and raw materials that affect the surface of the skin. What’s more, the technical skin substitute material can be modified and customised to suit particular purposes and requirements. For example, if the HUMskin is colonised with bacteria of human skin flora, microbiological tests can be carried out to find out how ‘safe’ and ‘effective’ an antibacterial product is with regard to skin flora, with no need for human volunteers. Odour testing, for example, on the rate at which perfumes evaporate can also be carried out realistically without using volunteers. Other options include simulating perspiring skin and applying artificial hair to the HUMskin. Thanks to such modifications, HUMskin can be perfectly adapted for any kind of testing. The technical skin model can be kept for longer than biological material (such as pigskin), so that the standardised tests can be reproduced at any time, without the use of human volunteers. It is significantly cheaper than trials involving human volunteers.

Claudia Balluff, Hohenstein Institute