Do Cosmetics Really Enter the Bloodstream?
- Your Cosmetic Chemist
- Sep 12
- 2 min read
The Truth About Skin Absorption: Do Cosmetics Really Enter the Bloodstream?
If you’ve spent any time online, you’ve probably seen claims that “everything you put on your skin goes straight into your bloodstream.” It sounds alarming—but it’s not accurate. The science of skin absorption is much more complex, and cosmetics are designed to work on the skin’s surface, not bypass its defenses. Let’s separate fact from fiction.
The Skin Barrier: Nature’s Shield
The skin is our first line of defense against the outside world. Its outermost layer—the stratum corneum—is made up of dead cells embedded in lipids, forming a dense barrier. This “brick-and-mortar” structure is extremely effective at blocking most substances.
For a molecule to even have a chance of moving beyond this layer, it usually needs to be very small—typically under 1000 Daltons in molecular weight. But even being small enough doesn’t guarantee that it will reach deeper layers.
Why Formulation Matters
Many skincare products are emulsions—blends of water and oil. Emulsions are useful because they can carry both hydrophilic (water-loving) and lipophilic (oil-loving) ingredients to the skin’s surface.
However, even with this delivery system, most cosmetic actives don’t travel far. After application, they may enter the stratum corneum, but navigating past tightly packed cells, lipids, and proteins to reach the dermis (where blood vessels are) is a monumental challenge.
Key Factors That Influence Absorption
Several variables determine whether an ingredient stays on the surface or penetrates further:
Molecular Size – Large molecules (over 1000 Daltons) typically stay put.
Polarity – Polar, water-soluble molecules struggle to pass through lipid-rich layers, while non-polar, oil-soluble molecules have better chances.
Solubility – If an ingredient isn’t compatible with the skin’s natural lipids, it won’t move past the surface.
pH – Human skin maintains an acidic pH (around 4.5–5.5). Ingredients outside this range interact less effectively.
The Bloodstream Myth
The biggest misconception? That skincare products “soak through” and circulate in the blood. In reality, cosmetics are not designed for systemic absorption.
Yes, transdermal drug delivery systems exist (like nicotine or hormone patches), but those are engineered with enhancers and specialized technology to bypass the skin’s defenses. Everyday cosmetics don’t have that capability.
For a substance to reach the bloodstream, it would need to pass through all skin layers and reach the dermis where blood vessels are located—a feat most cosmetic ingredients cannot achieve.
The Bottom Line
Cosmetics are formulated to improve the skin’s surface appearance and health, not to act as internal drugs. While certain small, well-formulated actives may penetrate into the upper layers of the epidermis, the leap to everything “entering the bloodstream” is far from fact.
The skin is an extraordinary protective barrier. Understanding how it works allows us to confidently use cosmetic products without falling prey to fear-driven misinformation. Always look for evidence-based information when evaluating claims about your skincare.

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