Your skin is one of your body’s first lines of defense against foreign invasion. We rely on it to keep us safe, clean, and pure. We rely on the skin’s natural barrier to act both as blockade and as a dam: keeping out dirt, germs, and pollution particles, and holding in necessary nutrients and water, not to be lost to the wind.
So if our skin is such an impenetrable force, then how is it that we use topical skincare products and hope that the effective ingredients reach their destination: deep within the skin’s layers? Because we rely on molecular biology and the physiology of our skin’s barrier function to work their magic.
Where do daltons fit in? What do they mean to your skincare, and why should you care?
What is a Dalton?
A dalton (Da) is a unit of measurement on a very small scale. It’s literally the standard used to measure mass at the atomic or molecular level. That’s pretty tiny! To put things in perspective, the molecular masses of proteins are usually expressed in kilodaltons (kDa). (One kilodalton is equal to 1,000 daltons.) Proteins are made up of tiny segments called amino acids, and the average molecular weight of an amino acid is 110 Da.
OK, fine, but when it comes to skincare, why should we care about daltons?
Daltons in Skincare
Because when it comes to ingredients that are going to be effective anti-aging, anti-acne, anti-inflammatory, and those that are going to provide nourishing benefit to the skin, those ingredients have to actually make it through the skin’s barrier to deliver their benefits. That holds true for ingredients that help our skin, and those that act as allergens and troublemakers.
What they (those experts) have found is that molecules that are larger than 500Da are not able to penetrate into the inner layers of the skin because they aren’t able to pass through the corneal layer. The phenomenon is known around skincare circles as the 500 Dalton Rule. It illustrates why some ingredients are able to seep all the way into the lower layers of skin, while others seem to just sit on top and not ever do anything. This is based off of a few things (Experimental Dermatology):
1. Nearly all of the contact allergens that scientists know of are small than 500 Daltons.
2. The most common pharmaceutical ingredients applied topically are under 500 Daltons.
3. Effective drugs that contain a transdermal delivery system are under 500 Daltons.
While there are some exceptions relevant to skin care— allergies to latex (over 50,000 Daltons) and the successful use of tacrolimus (822 Daltons) to treat certain skin conditions, for example — overall, the 500 Dalton rule appears to be a good general rule of thumb. This is because we know that something under 500 Daltons will be able to cross the skin barrier effectively. We have not yet discovered the method that allows anything over 500 Daltons to cross the skin barrier.
The Workings of Your Skin
Your skin is composed of three main layers from outer-in: the Epidermis, Dermis, and Hypodermis. The epidermis is further broken down into several layers, the stratum corneum being the outermost. Made up of mostly dead epithelial cells, it serves as the main boundary. Here is where most foreign objects are stopped in their tracks. This layer is tough and mostly waterproof.
That’s good news, unless you’re looking to have beneficial treatments delivered to the inner layers of your skin. In order to get through, molecules have to pass between the tough skin cells. That’s an easier task if they attract fat (are lipophilic), as cell membranes tend to repel water.
The biggest holdup in getting through the skin is the actual size of the molecule. Anything smaller than 500Da will be able to squeeze itself in between the skin cells and traverse through the layers. Think of it like a tiny mouse squeezing itself into a little mouse hole. His cousin, the guinea pig, while small, can’t fit through the same little space.
Research has proven this time and again. Any allergens that cause skin irritation have to be able to penetrate the skin to cause the immune response. All known allergens have been found to be smaller than 500Da. In addition, the most commonly used (effective) topical drugs in dermatology are also known to be less than 500 Da. Both allergens and medications must be able to penetrate the skin in order to cause the immune response, whether good or bad.
What Do Daltons Have to Do With Skincare?
The answer to that question depends on what it is you’re trying to accomplish with your skincare products. Some products don’t need to penetrate into the deeper layers in order to be effective. These include occlusive creams designed to prevent water loss. These moisturizers and some serums will do their job best by sitting on the top layer.
Products that are designed to work on a more molecular level should be smaller since they need to reach deep into the skin’ layers in order to take effect. Knowing how big these molecules really are can help you determine if these products will be as effective as they claim to be! For instance, retinoic acid or retinol, used as popular anti-aging treatments are known for being incredibly effective at what they do. When you look at the molecular weight of each of them, they’re 300Da and 286Da, respectively.
Let’s Talk About Peptides
The major issue comes when you’re dealing with ingredients like peptides. By the 500 Dalton rule, peptides should not be absorbed in your skin and, subsequently, should not be effective. However, despite the fact that peptides are greater than 500 Daltons, there are several studies that suggest peptides are helpful when applied topically. For example, double-blind study with a control group that had participants apply different things to each side of their face found that palmitoyl pentapeptide-3 effectively increase the production of collagen and of extracellular matrix proteins (International Journal of Cosmetic Science). Another study found that when palmitoyl oligopeptide stimulates collagen production in skin fibroblasts when used twice a day for six months (Dermatologic Therapy). And palmitoyl oligopeptide has been shown to down-regulate elastin
In general, some dermatologists say peptides don’t work as a result of this, and dismiss them, like Dr. Leslie Baumann, MD. “Many active ingredients that are used as “buzz words” in skin care cannot penetrate the skin, leaving them useless, for instance: oxygen, stem cells, hyaluronic acid, and peptides,” Dr. Baumann said. However, other researchers believe that peptides may work by increasing the penetration of other beneficial ingredients into the skin (Nature Medicine, Molecular Pharmaceutics). Still others believe peptides might work by signaling to crucial proteins while laying atop the skin itself (Experimental Dermatology). At this point, however, it’s altogether unclear.
I personally like peptides, and use them regularly, but this 500 Dalton Rule should be kept in mind.
Bottom Line
If you aren’t sure of a new product, doing just a little bit of research beforehand can go a long way towards making sure you’re getting what you’re paying for. You just have to consider what it is the product will be doing, where it needs to penetrate to (if at all), and the molecular weight in Daltons. If It’s something meant to affect the deeper levels of your skin, a good way to determine if it deserves further consideration is to make sure it’s smaller than 500 Daltons.