What Affects Absorption Through Skin

Whether anything crosses skin depends on a short list of factors. Understanding them is the best defence against overstated patch marketing.

MOLECULAR SIZE. This is the dominant factor. The outer skin layer permits small molecules far more readily than large ones, and the practical ceiling is low. Vitamin B12, the largest and most structurally complex vitamin, sits well outside the range usually described as favourable.

CHARGE. Neutral molecules cross more readily than charged ones. This is why mineral ions — magnesium, sodium, potassium — are difficult cases, and why widespread claims about minerals absorbing through skin are not well supported.

SOLUBILITY BALANCE. A molecule needs enough fat solubility to enter the lipid-rich outer layer, and enough water solubility to move out of it into the tissue beneath. Extreme in either direction is unfavourable. Caffeine's reasonable balance in both is why it comes up so often in this conversation.

DOSE AND CONCENTRATION. A larger quantity in the patch does not translate proportionally into a larger amount crossing. The barrier does not scale politely.

APPLICATION SITE. Skin thickness varies substantially across the body. Hair follicles, sweat glands and local blood flow all differ by site, which is why patch instructions specify where to apply.

TEMPERATURE AND HYDRATION. Warm, well-hydrated skin behaves differently to cold, dry skin. This is one reason individual and day-to-day variation is real.

TIME. Contact duration matters, which is why every patch specifies a wear window.

None of these factors let anyone state a percentage without measuring it in that specific formulation. When a brand publishes an absorption figure with no study behind it, the figure is invented. VYROTECH publishes what is in its patches and declines to publish numbers it has not measured.