Why molecular weight matters?Updated a year ago
With all skincare ingredients, the weight of the individual molecules plays a big role in how the molecule will penetrate through the skin, or if it will penetrate at all. Molecular weight is measured with a unit called the dalton.
Most skincare products are formulated to impact the stratum corneum, which is the outermost layer of the skin and is largely comprised of anucleated skin cells (i.e., largely inactive cells with limited biological activity but important protective effect.).
For an ingredient to penetrate beyond the stratum corneum into the lower layers of the epidermis, it needs to have a lower molecular weight.
Normally, we want our skincare actives to have a lower molecular weight, because we want them to impact the lower levels of skin. Retinal, the skin-transforming powerhouse in our Enzyme-Active Retinol Serum, has a molecular weight of approximately 284 daltons, while ascorbic acid has a molecular weight of around 176 daltons.
However, in the case of certain ingredients, the molecular weight directly corresponds with irritation. For example, sodium lauryl sulfate with its 288 daltons is a major potential irritant. It’s almost exclusively used in cleansers, where the risk is mitigated by washing it off. Even so, it’s becoming less popular and many brands choose to leave it out of their formulas.