Topical and transdermal: what changes?

Topical describes application to a body surface, commonly the skin. In product development, a topical product is often designed to act locally. Transdermal describes delivery through the skin to the wider body. Two words, two destinations.

Start with the intended destination

Two questions are worth keeping apart: where is a product applied, and where is it designed to act? A cream or gel is a format. A patch is also a format. The formulation inside each one is built around its destination.

The FDA draws the same line in its 2019 draft guidance for medicinal delivery systems, between systems intended for local delivery and systems intended to deliver an ingredient through the skin to the whole body. It is guidance for medicines, cited here as background science. Read the FDA draft guidance.

On skin, in skin and through skin

These short phrases describe different observations:

• On skin: the formulation is in contact with the surface.
• In skin: an ingredient has been found within a skin layer.
• Through skin: a measurement shows passage across the skin in the conditions tested.
• In the body: studies in people measure the ingredient in blood samples.

A laboratory skin experiment and a human blood study are both valuable, and each answers its own question. OECD Test Guideline 428, for example, describes experiments using a skin sample held between two chambers; researchers analyse the skin and the collecting fluid. See the OECD laboratory method.

Gels, tablets and patches: which route?

Comparisons often group tablets, capsules and gels together, so check how each product is used. A swallowed gel follows the oral route; a skin gel sits on the skin. “Patch versus gel” is often a comparison of two products applied to skin, rather than a comparison between skin and digestion.

That small distinction keeps a buying decision grounded in the products in front of you. Compare instructions, composition and purpose, and choose the format that suits your day.

The most useful question to ask

When you see the word “transdermal”, ask what sits behind it: a general mechanism, a laboratory test of a formulation or measurements in people. Each layer adds something, and a clear brand makes it easy to see which is which.

At 24/sync we keep it simple. A clear patch, with actives built into the adhesive layer that sits against your skin, designed to release steadily across the wear time. Every ingredient and amount is on the label, down to the milligram.

Choosing with the right expectations

A wearable format appeals because there is nothing to swallow, mix or brew, and it travels with you. That practical preference is reason enough. Everyone's different: give it a couple of weeks of daily wear and notice how your days feel.

For a closer look at the route itself, read your skin barrier, explained. For what goes into every 24/sync patch, visit Science & standards. Our patch guide covers practical use.