Skin Care Products - How Much Gets In?
by Karin Parramore, CH
In our increasingly polluted modern world, it is important to do all we can to avoid increasing the toxin load in our bodies. More and more people are choosing to eat organically grown foods and drink clean water, and many people choose to use all natural skin care products as well. While it is easy to understand why we should choose organically grown foods, just how important is it to avoid synthetic ingredients in body care products? An understanding of the nature of skin, and how ingredients in skin care products might actually penetrate the skin to be delivered into the blood stream, can help us see why, in my opinion, it is imperative we avoid synthetic ingredients at all costs.
Any discussion of transdermal ("across the skin") absorption requires at least a rudimentary review of the nature of skin, so here we go--skin 101! The skin is made up of several layers. The basic divisions are the epidermis (the part we usually think of as our skin because it is the part we can touch), the dermis (where most of our blood vessels live), and the subcutaneous tissue. The outermost layer of the epidermis, called the stratum corneum, is made up of cells high in keratin, a substance that helps maintain skin hydration by reducing moisture loss—in effect, keratin contributes to the creation of a semi-waterproof barrier. This hydrophobic ("water-fearing") layer sits just on top of a hydrophilic ("water-loving") layer which readily accepts water and water-based substances.
How is it possible to get water past the stratum corneum, that supposedly waterproof layer? Well, interestingly enough, the more the cells of the stratum corneum are exposed to water, the more permeable they become. The wrinkles we get on our fingers after a long soak in the tub result from water being absorbed into the skin, across the stratum corneum, to the water-loving layer beneath. Recent studies have shown that hydrated skin is 3.3 times more likely to absorb substances across its surface.1 Clearly, our skin is responsible for letting substances in as well as keeping them out, and the active function depends largely on the environment in which the skin finds itself.
But really, how often do we stop to think about this process? Many of us slather lotion all over our skin to moisturize but rarely do we give a thought to what is happening when we do.
Lotion is a water and oil emulsion. Because water and oil don't mix, an emulsifying agent is added to the water and oil components in order to encourage them to get along happily and not separate. Once the product is applied to the skin, however, the innate nature of these two ingredients takes over, and they start to follow their basic natures. The oil component now finds itself in the position to escape, to migrate away from water, and toward other fatty components, namely the sebaceous (oil) glands found in the dermis, and subcutaneous fat found just below the dermis. In a way we can see that the water component of the lotion to some degree helps drive the oil into the skin by repelling the oil.
Despite how this sounds, the process is not active; substances are passively diffused across the skin and into the bloodstream over time. This means the substance must remain in contact with the skin for quite a while to be absorbed, as passive diffusion is not instantaneous.2 Something like a lotion, which remains in contact with the skin and is often re-applied, is probably one of the better ways to encourage active ingredients to migrate through the skin and into the bloodstream.
Regardless of the vehicle, however, not all ingredients are capable of crossing this barrier. Here is where the molecular weight of an ingredient comes into play. Without getting too technical, it helps to understand that in order to easily cross the skin a substance must have a molecular weight of less than 500 Daltons (a Dalton is the unit of measure for molecular mass).3 Essential oils, which are not "oils" at all but are actually closer to alcohols in their characteristics, are often added as ingredients in high quality skin care products. All essential oils are characterized by a Dalton weight below 500. This means that all of the wonderful effects associated with essential oils cross quite readily into the bloodstream.
Fixed oils like almond or olive oil, however, which form the base of most lotions, usually have a higher molecular weight, somewhere around 800 Daltons. This means if fixed oils are absorbed at all the rate is extremely slow. Consequently, these oils will sit on the surface of the skin and act to lubricate it, the reason we use lotions in the first place.
Of course, many lotions contain ingredients other than fixed oils and essential oils; namely, synthetic fragrances and preservatives. So how does the barrier function of the skin respond to these substances? Are they hydrophobic? What is their molecular weight?
Well as it turns out, unfortunately, most of these types of substances easily cross the skin and are readily taken up into the bloodstream. The sudden upsurge in estrogen and progesterone patches in recent years is testament to the fact that these types of substances, namely, steroidal (hormonal) substances, quite readily cross into the bloodstream. 4 The only limiting factor seems to be how lipophilic ("fat-loving") they are.5 In a medium like lotion, where at least 50% of the product is oil, we can safely assume the lotion acts as both a carrier and a delivery system for steroidal compounds.
But really, is this any surprise? Our entire body communication system is based on hormones, both internally generated and those we receive from outside ourselves, like those from foods. Further, consider the fact that pheromones, those odiferous messengers of our body's native signaling system, leave our bodies to do their work via the skin. As their name suggests, pheromones are hormones; specifically, steroidal hormones. If our skin were resistant to the passage of hormones, we would never be able to send molecular messages to the outside world. (Despite the modern prudish attitude toward body odor, we are physiologically programmed to tell a potential mate we are interested via scent). It flies in the face of evolutionary theory to block hormonal signaling at the skin.
In the case of synthetic fragrances, which have been shown to disrupt normal hormonal function6, we have to further consider that a percentage of these molecules volatize into the air and enter the nose, where they are easily absorbed through the olfactory bulb, the part of the brain responsible for our sense of smell. Not only are we receiving them into the bloodstream via topical application, but we are getting a direct dose to the brain via the olfactory. If our entire communication system is based on the signals sent by hormones, what are we doing to ourselves by applying these synthetic steroidal-like compounds?
This information about the nature of our skin gives us a big clue toward understanding how ingredients in skin care products actually penetrate the skin and enter the blood stream. If we are trying to maintain a toxin-free body, clearly it is a wise decision to choose natural and organic body care products.
2. Physicians' Desk Reference, 57th ed. Thomson PDR, Montvale, NJ 2003
3. Gennaro, AR, Ed., Remington's Practice of Pharmacy, 20th ed. Baltimore, MD: Lippincott Williams & Wilkins, 2000 p. 836