106 SUN CARE
The forgotten destruction The skin cannot withstand efficiently the aggressive power of the sun. Without the skin microbiota, the skin would be even more defenceless. The scientific literature describes countless mechanisms by which sunlight damages the skin. The disrupting mechanisms on keratinocytes, skin lipids, collagen, fibroblasts and immune cells are extensively researched. When it comes to the influence of sunlight on the skin microbiota, scientific literature remains dormant. When some studies can be spotted, they
usually investigate the influence of UV light on the skin microbiota. However, sunlight is not solely UV light. Indeed, sunlight consists of only 3-5% UV light. The majority is infrared light (52-55%) and the rest is visible light. The influence of infrared light cannot be neglected as microorganisms always suffer under heat stress. Heat can kill microbes by altering their membranes and denaturing proteins. The skin microbiota, unlike the other skin
layers, sits on the first row when the blast of sunlight hits the skin surface. In the following in vivo studies, the viability and the composition of the skin microbiota are monitored.
The viability of the skin microbiota under sun exposure To investigate the viability of the skin microbiota under sunlight, the following test was conducted. The forearm of seven volunteers was exposed to the sun at 11am during the month of June. Before the test, none of the test persons were exposed to sunlight for 24 hours. The time of exposure varied from 60 minutes, 30 minutes, 20 minutes and 15 minutes. The rest period between the two tests was one week. To quantify the skin microbiota, an Agar-TTC
slide was pressed firmly for one minute over a skin surface of 10 cm2
. The quantification of
the skin microbiota was performed prior to the exposure and immediately after the exposure. The bacteria and fungi were monitored separately. The initial measured concentration was equated to 100%. It was estimated that the initial concentration over all the individuals varied from 103 to 104 CFU/cm2
Without HMW Inulin-SPF30 ■ With HMW Inulin-SPF30 ■
100 90 80 70 60 50 40 30 20 10 0
T: 0min
T: 20min Figure 2: The influence of an SPF30 sun cream on the viability of the skin microbiota
TABLE 1: THE COMPOSITION OF THE TESTED SPF SUN CREAMS
Ingredients
Aqua HMW Inulin Glycerin
Preservative
SunZno SA (Zinc Oxide, Stearic Acid)
Neocare P3R (Polyglyceryl-3 (Poly) ricinoleate)
Miglyol 812 (Caprylic/Capric Triglyceride)
Cetiol V (Decyl Oleate)
Gosulin IL MB (Isoamyl Laurate)
Placebo - 3% 0.8%
19.25% 3%
5.5% 6% 9%
HMW Inulin
2% 3%
0.8%
19.25% 3%
5.5% 6% 9%
and UV light destroyed the skin microbiota. In this study, the skin and of course the skin microbiota were not shielded from UV light by a sun protection cream.
for bacteria and
102 to 103 CFU/cm2 for fungi. The results (Figure 1) show that on the skin of
all the volunteers, none of the microorganisms could be detected, which indicates that all fungi and bacteria died. The combination of infrared
The influence of an SPF 30 sun cream To investigate if a sun cream SPF 30 improved the viability of the skin microbiota under sunlight, the following test was conducted. The formulation of the sun cream is set out in Table 1. Seven volunteers were exposed to the sun at 11am during the month of July. One forearm was exposed without the sun cream, while the other forearm was treated with the sun cream; 2mg/ cm2
was applied. Without HMW Inulin-SPF30 ■ With HMW Inulin-SPF30 ■
100 90 80 70 60 50 40 30 20 10 0
T: 0min T: 20min T: 2h T: 4h
Figure 3: The evolution of the viability of the bacteria of the skin microbiota with and without HMW inulin
PERSONAL CARE March 2024
100 80 60 40 20 0
-20 -40 -60
Before the test, none of the volunteers were
exposed to sunlight for 24 hours. The time of exposure was 20 minutes. To quantify the skin microbiota, an Agar-TTC slide was pressed firmly for one minute over a skin surface of 10 cm2
. The quantification of the skin microbiota
was performed prior to the exposure and immediately after the exposure. The bacteria and fungi were monitored separately. The initial measured concentration was equated to 100%. The results (Figure 2) show that in all
volunteers again none of the microorganisms could be detected, which indicates that most likely all fungi and bacteria died. The protective skin microbiota had vanished.
The support of a prebiotic Prebiotics might support the skin microbiota under sun exposure. Prebiotics are polysaccharides that support solely protective members of the skin microbiota. Prebiotics do not support pathogens or the transient microbiota. The transient microbiota occurs rather by accident on the skin. Usually, these microorganisms come from the environment. They mean no harm, but they also have no beneficial effects on the skin and the skin microbiota. Inulin is such a polysaccharide. It is a
naturally occurring polymer from fructose. Although fructose can support almost all microorganisms, including pathogens, the fructose in inulin is bound in such a way that a special enzyme is needed to unlock it. Most microorganisms, such as pathogens and transient microbes, do not have this
Without HMW Inulin-SPF30 ■ With HMW Inulin-SPF30 ■ 88
25 33 21
-40 Cutibateria -57
-47
-55 S. epidermidis Corynebacteria Micrococcus
Figure 4: The evolution of the composition of the skin microbiota with and without HMW inulin
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Relative amount of bacteria and fungi
Relative amount of bacteria and fungi
Change in %
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