What do we know,
and what don't we know yet?
We read 28 scientific papers on prebiotic skincare and the ingredients in our cream. Next to every piece of information, we've noted how strong the evidence behind it is and where it falls short.
- 01
The outermost layer of the skin keeps moisture in.
This layer is made up of cells and the fats that fill the gaps between them. It is mainly these fats that stop moisture from escaping.
Strong evidenceAn established fact of skin science.
- 02
Hot water, harsh cleansers, dry air and shaving wear the skin out.
Skin washed in water at 40 degrees loses more water than skin washed in water at 20 degrees. Harsh cleansers strip away the skin's fats. Dry, cold air weakens the skin's protective layer. Shaving also takes a thin layer off the very surface of the skin.
Strong evidenceThe effect varies from person to person and with how much exposure there is.
- 03
The microorganisms on the skin help protect it.
A community of microorganisms all of its own lives on the skin's surface. The more diverse this community is, the better the skin's protective layer works. A bacterium that lives naturally on the skin has been shown to help produce the fats that hold in the skin's moisture.
Limited clinical evidenceSome of these findings come from animal studies.
- 04
Prebiotics can be applied to the skin, too.
By the international definition, a prebiotic is a substance used by the body's beneficial microorganisms that brings a health benefit. This definition also covers products applied to the skin.
Strong evidenceThis is a definition; the effect of each product has to be shown separately.
- 05
Prebiotics may support the beneficial species living on the skin.
In the lab, some prebiotics supported the skin's beneficial bacteria while pushing unwanted bacteria into the background. This effect held up inside cream and gel formulas, too.
Laboratory levelThese are laboratory studies; whether the same happens on the skin still needs to be shown separately.
- 06
Prebiotics applied to the skin may increase moisture and reduce water loss.
In a study of 60 people, those using a prebiotic serum had more hydrated skin after 8 weeks than those using an inactive serum. In a study of 110 people, moisture rose within 28 days. In a study of 140 people, a prebiotic skincare routine reduced dryness in 4 weeks.
Limited clinical evidenceThe studies are small and each used a different prebiotic. Some had no comparison group.
- 07
Prebiotics may help a worn barrier recover.
When a sugar with prebiotic properties (xylitol) was applied to human skin worn down with tape, the skin's protective layer recovered faster.
Laboratory levelA small study looking at the mechanism.
- 08
The overall picture on prebiotic cosmetics.
Recent reviews find the early results for prebiotics applied to the skin promising and say they do not disrupt the skin's natural make-up.
Limited clinical evidenceThe studies are small and differ from one another; there is no common yardstick yet.
Key terms
Skin barrier
The outermost layer of the skin. It is made of cells and the lipids that fill the spaces between them; it keeps moisture in and protects against outside factors.
Prebiotic
A substance that is selectively used by the body's beneficial microorganisms and confers a health benefit. It can also be applied to the skin; it is not alive.
Probiotic
A live microorganism that confers a benefit when applied in adequate amounts.
Postbiotic
Substances produced by microorganisms, or inactivated parts of microorganisms.
Skin microbiome
The community of microorganisms living on the skin. Most of them do the skin no harm and work together with its protective layer.
Transepidermal water loss (TEWL)
The amount of water evaporating from the skin into the air. It is the most common measure of how well the skin barrier is working; lower is better.