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Ask a Skin Care Biologist is a recurring Bioluminescence post where OUMERE's CEO and CSO, Wendy Ouriel, M.S., answers your skin care questions. Wendy is a cellular biologist with expertise in cellular aging, extracellular matrix biology and the biology of skin care.


- Carrie L.

It’s a running joke for whomever knows me that I am such a skin care purist that I even consider water bad for the skin. I think the jokes are apt because I come off as a bit eccentric until you hear me out:

1. Water is necessary for survival and if we don’t drink water we will die within a few days. We also need water externally for hygiene, and I am not advocating for milk or tea baths. However, when it comes to skin care we need to be careful with how we use water for the following reasons:
Water has a pH of 7, your skin has a pH of ~4.9-5.5
One of the causes of acne, skin dryness, contact dermatitis, pre-mature wrinkling and other skin concerns is due to the disruption of skin’s pH, which acts as a protective barrier. The reason why it is paramount that your skin care is on the acidic side is because raising your skin’s pH will break down that protective barrier. Alkaline, foaming cleansers, as we all know are damaging, acne-causing, and stripping for this very reason, because they are alkaline and raise your skin’s pH. It is not easy to lower your skin’s pH back to a healthy level if you are constantly using alkaline products, which is why you see long-term skin issues, such as acne, arise from bad skin care. Water, although a weak base, is still a base, and will raise your skin’s pH and cause the breakdown of your skin slightly with each contact. Over years this accumulates in the form of damaged, aged skin.
For this reason, I recommend only introducing water into your skin care routine when it is mixed with another product as a diluent, and when rinsing off your (acidic) cleanser.
2. Water used during a skin care regimen is usually hot or warm
If you rinse your face with hot or warm water, you are stripping your skin, and putting yourself at risk for broken capillaries and collagen breakdown.
When you take a hot shower or rinse your face with hot or warm water, your skin feels tight. This is the moisture and oil being pulled from your skin. Depending on your skin type, stripping your skin of moisture and oil will either result in dryness (which causes pre-mature wrinkling) or over-production of inflammatory sebum (which causes acne and other skin diseases).
The heat also weakens the capillaries in the areas of the skin that are thin, such as around the eyes, and can denature proteins such as collagen and elastin.

** Under no circumstances should hot water or steam ever be applied to the face because this will inflame and damage the skin in addition to exacerbating (or creating) skin disease.

3. Tap water contains impurities Most people do not keep a gallon jug of distilled water by their sink to rinse their skin after cleansing, but if you have any type of irritated/disrupted skin, whether it is general skin sensitivity, rosacea, dryness or acne, you should only be using cold distilled water to rinse your skin.

Tap water impurities include:

Inorganic chemicals such as copper, fluoride, chlorine, arsenic, asbestos, lead, and mercury.

Organic chemicals such as benzene, toluene, vinyl chloride and xylene

Microorganisms and viruses (vary depending on region).

Tap water has a relatively low amount of the above-mentioned impurities, and the EPA has regulations for American tap water to ensure the water you are drinking is safe. However, applying water to the skin with the above impurities will make existing skin conditions worse. I recommend using only distilled water, which has most of the common impurities from tap water removed.

If you have any sort of skin sensitivity you should only be using distilled water to rinse off your cleanser, and should not expose your skin to water at any other time.


- Hoda S.

I frequently discuss the importance of maintaining the skin microbiome with properly formulated skin care because it is a central aspect of skin health. Your skin microbiome contains beneficial bacteria that provide protection against skin-damaging bacteria. A disruption of the skin microbiome can lead to dermatitis, acne and eczema.

The mutualistic symbiosis is not limited to skin, there are beneficial bacteria throughout your body. One example is the bacteria in your gut, which is necessary for digestive health. Having a disruption in gut bacteria can lead to a slew of stomach and digestive illnesses, which is why probiotics in the diet are essential.

Does it reason that probiotics in skin care are also beneficial?

For this to be the case, 3 things must occur:

1. The bacteria in the skin care must not harm the beneficial bacteria comprising your skin’s microbiome

2. The bacteria in the skin care must be incorporated into the microbiome


3. The bacteria from the skin care, once incorporated, must be able to have a symbiosis with the present bacteria with the overall function of maintaining your skin’s health.

It appears that the data is far from conclusive on probiotics in skin care and there is a long way to go before I can draw any conclusions. There is not enough sound, published data on the topic. However, a few notes:

  • Everyone’s skin microbiome is different, and what may be beneficial for some may cause damage to others.
  • Your skin is much more delicate than your stomach, and may be sensitive to the introduction of bacteria in an unnatural manner, such as through skin care. Your skin can also not break down harmful bacteria with the same efficiency as your stomach
  • It may be safer to just maintain the microbiome you already have by using beneficial skin care that maintains your skin’s protective barrier. The gold standard is daily chemical exfoliation.
Bacteria and fungus found on the surface of human skin. SEM image.


- Olivia F.

Sunscreens are pharmaceutical and need to be considered as such, even when they are in your skin care or makeup. For any pharmaceutical, there is a dosage, and you need to take that dosage in order to get the full effects of the drug.

For a sunscreen, you need to have 1/4 tsp of product on your face to have the advertised SPF. If you get any less sunscreen you are going to get less protection.

The problem is that most people do not use 1/4tsp of foundation or moisturizer on their face, so while the moisturizer or foundation offers sun protection, you are likely getting far less protection than advertised and are putting yourself at risk for skin cancer and UV-induced photo-aging.

Furthermore, moisturizers, foundations and other cosmetics with sunscreen do not always have broad spectrum protection. So while they may block out the rays that burn (UVB) they will not block out the rays that cause aging (UVA). And both rays need to be blocked to prevent skin cancer.

I recommend using pure sunscreen on your face, neck and any part of the body exposed to the sun throughout the day and not relying on what is in cosmetics because the protection is likely to be far less.

Have a question that you would like answered in an upcoming Ask a Skin Care Biologist post? Submit them to


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