Is there a humectant tipping point where they dry out the skin?

What are humectants?

Humectants hold water and attract water to them. Examples include vegetable glycerine, propylene glycol, propanediol 1,3, sodium lactate, sodium PCA, hyaluronic acid, panthenol, urea, and more. Different humectants have varying levels of strength and other strengths and weaknesses. Humectants are applied to the skin as part of complete skincare products that typically include other ingredients like water, emollients, and actives. Like many cosmetic ingredients, they should not be applied undiluted to the skin. For most people, they are not a stand-alone solution to dry skin, but they are usually part of a dry skin solution. Generally, you’ll want to pair humectant-rich products with more emollient/occlusive products to further slow water loss.

What do humectants do in our products?

One of the biggest functions humectants play in our products (as opposed to in skincare) is they keep ’em from drying out too fast. They slow evaporation of the water in the formula—both in storage and on application. They can also help boost preservative function, depending on concentration (this varies by humectant—propylene glycol has 3–4x the antimicrobial effects that glycerine has).

The skin, water, and humectants

While the outer layers of the skin will happily absorb lots of water (think of your hands going all wrinkly in the bath), the skin doesn’t do a great job of holding onto that water, especially in dry environments as the outermost layers of the skin maintain equilibrium with ambient humidity. This means if you live somewhere with low ambient humidity, your skin is not going to stay super hydrated on its own (regardless of how much water you drink—more on that in the next paragraph). Excess water (including the water in our lotions/serums/etc.) evaporates off the skin pretty quickly, temporarily increasing transepidermal water loss (TEWL). Humectants can help slow this loss. According to Harry’s Cosmeticology, “there is no factual foundation for the idea that humectants attract water our of the air and deliver it to the skin.”

The human vascular system stops at the dermis—one full layer beneath the epidermis (the top layer of the skin)—meaning the body’s ability to deliver water to the epidermis isn’t great as the “train lines” stop well before reaching the stratum corneum (the top layer of the epidermis). Applying humectants to the skin can help draw up moisture from the dermis, which is generally a good thing—assuming you aren’t hugely dehydrated + the skin barrier (also known as the acid mantle) is functioning well, keeping transepidermal water loss (TEWL) to a minimum. If the barrier is damaged it is possible that the water pulled up from the dermis by humectants will evaporate quickly, leaving the skin just as dry as it was before (if not drier). This water loss can be slowed by ensuring moisturizers also include emollients (like liquid oils and butters) and occlusives (like petrolatum).

Can high concentrations of humectants steal moisture from the skin, making it drier?

  • This could be problematic if you applied pure humectants with no water, but that’s not really done. Humectants are usually applied as part of a product that contains its own water (hyaluronic acid serums usually contain 1% or less hyaluronic acid—there will be plenty of water in the formulation!). The humectants in the formulation will help slow the evaporation/loss of that water, both in the bottle/tube and once applied to the skin.
  • Unless you are severely dehydrated (in which case I’d say you have bigger problems than dry skin!), the vascular system continuously delivers water to the dermis. Having that water pulled up into the outer layers of the skin by humectants is not depriving any part of your body of water.
  • While humectants can slow the evaporation of water from the skin, you’ll still want to pair them with something that contains oil to further slow evaporation. An emollient lotion or oil serum will help, as will occlusives like petrolatum (Vaseline/petroleum jelly).
  • If the humectant is on your skin it’s not “stealing” water from the skin for itself—it’s keeping it around for longer, in direct contact with the skin.

Further reading

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