Let’s focus on the skin’s barrier function.
Imagine if everything we put on our skin went through. Or worse, our insides started leaking out. Very dangerous, and pretty gross.
Your skin’s barrier function is crucial for survival. Thankfully, healthy skin is an effective barrier to many particles, chemicals and microorganisms. It’s the top layer, the stratum corneum, that plays the vital role in this barrier function.
The skin barrier works in two directions:
• It keeps water in. Without this, we’d literally dry out. Our cells and organs need that moisture to stay alive and healthy.
• It keeps things out. Think microorganisms, irritants, chemicals and the sun’s UV rays (although of course these can damage the skin). Only some things we touch are able to penetrate our skin. These are limited to very small molecules and those with particular water and oil solubility characteristics.
The challenge of transdermal drug delivery
Think how easy medicine delivery would be if it could be applied via the skin. No pills, suppositories, needles or IVs needed!
A whole area of drug delivery research is focused on overcoming the formidable challenge posed by the skin barrier.
There are two potential ways that a drug could cross the healthy skin barrier: through the stratum corneum (either through the cells or between them), or via sweat glands and hair follicles.
Drug molecules need to be small enough and have adequate solubility in both oil and water AND the drug needs to have suitable pharmacological activity when it gets through.
The skin can also fix itself! When the stratum corneum is damaged, the skin accelerates processes to repair the damage and restore the barrier properties.
