Transdermal

Transdermal means absorbed through the skin. Transdermal hormones are patches, gels and sprays, available for both [estradiol](/glossary/estradiol) and testosterone, and they reach the blood without passing through the liver first.

Where you'll meet it

When choosing a form of estrogen or testosterone, and especially in conversations about clot risk, where transdermal estradiol is often recommended over tablets. You will also see it on pharmacy labels and in the names of products, and in the instructions about washing hands and covering skin that come with testosterone gel.

What it means for estrogen

Estradiol swallowed as a tablet goes from the gut to the liver before reaching the rest of the body. That first pass through the liver raises the clotting proteins made there, and raises SHBG. Through the skin, estradiol skips that step.

That is why prescribers often suggest patches or gel for people over about 40, smokers, people who are overweight, and anyone with a past clot or a family history of DVT. It is one of the few clot-risk levers you and your prescriber control directly. Injections also skip the liver, but swing more between peak and trough. Estrogen compares the routes.

What it means for testosterone

For testosterone the case is less about the liver and more about steadiness. Daily gel gives the flattest levels of any common form, with no end-of-cycle dip, and suits people who hate needles. Testosterone covers how it compares with injections.

How it is taken

• Gels go on once a day, on clean, dry skin, at roughly the same time each day, and need a few minutes to dry before you dress. Where they go (arms, shoulders, belly or thighs) depends on the product.
• Sprays work like gels in a smaller volume, and exist for estradiol in some countries.
• Patches stay on for a few days and are then replaced, usually on the lower belly or buttock, moving the site each time. They can peel, irritate the skin or come off in heat, sweat or water, which matters if you live somewhere hot or swim a lot.

Absorption through skin varies more between people than with injections, so some people struggle to reach their target level on a patch or gel. That shows up on blood tests, and the answer is a conversation about the route, not piling on more product.

Protecting other people

Gel on your skin can transfer to anyone who touches it before it has dried and been covered, including partners, children and pets. With testosterone gel in particular that can affect them, and children are most at risk. Let it dry, wash your hands, and keep the area under clothing. Pick one application site and one time of day so it becomes automatic.

Blood tests on transdermal hormones

Have blood taken from the arm you did not apply gel to, or from a different site. A sample drawn through skin with gel on it can come back falsely high, sometimes wildly so. How to read your hormone blood results covers timing for each form.

Common questions

"Transdermal is weaker." It is a different route, not a weaker one. The target levels are the same.

"No clot risk at all." Lower than tablets, not zero. Smoking, surgery and long flights still matter; hormones and surgery explains the planning around operations.

What to ask

Ask whether a transdermal form would lower your particular risks, how well it tends to reach target levels in the prescriber's experience, and what the cost difference is where you live; patches in particular can cost more than tablets.

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