Does cysteamine work as well as hydroquinone?

Comparison studies reported results in broadly the same range over several months. Those trials were small, so treat it as a credible alternative rather than a proven equal.

Why does it smell like that?

It is a thiol, and thiols smell of sulphur. Formulators mask it imperfectly, and the smell is the single most common reason people stop using it — worth knowing before you buy rather than after.

How long do I leave it on?

The published protocol applies it to dry skin for about fifteen minutes and then washes it off. Longer contact was not what was tested and mostly buys irritation.

Is it safe during pregnancy?

There is no topical safety data in pregnancy, so it is not an ingredient to start then. Melasma often flares during pregnancy, and that is a conversation to have with a clinician.

How long before I see anything?

The trials measured change over months rather than weeks. If nothing has shifted after a few months of consistent use with genuine sun protection, the answer is a clinical review, not a higher concentration.

Cysteamine — Ingredient Guide

How it works

Cysteamine is an aminothiol the body produces itself, as a breakdown product of coenzyme A. Applied to skin, it acts on pigment production at several points rather than one: it inhibits tyrosinase and peroxidase, it chelates the copper that tyrosinase depends on, and it raises intracellular glutathione, which shifts melanin synthesis away from the darker eumelanin. Which of these does most of the work has not been settled, and an honest description is that it interferes broadly rather than precisely.

The evidence

Unusually strong for a pigment ingredient available without a prescription. Randomised, placebo-controlled work using a 5% cream reported lower pigmentation scores over several months of use, and comparison work against prescription hydroquinone reported results in broadly the same range.

Two caveats belong beside that. The trial populations were small, and every protocol included strict sun protection, which is doing part of the work in the results. And melasma is a chronic, relapsing diagnosis driven by ultraviolet exposure and hormones — no topical resolves it permanently, returning pigment is the expected course rather than a product failure, and a pattern that is spreading or changing deserves a diagnosis rather than another jar.

Suitability

Facial hyperpigmentation, including melasma, where the diagnosis is already established
People avoiding hydroquinone, or who have used it and want an alternative
Not on broken, inflamed or actively dermatitic skin
Introduce it on its own — establishing tolerance while running an aggressive acid routine tells you nothing

Concentration

5% is the concentration used in the published trials, and it is applied in a specific way: to dry skin, left for roughly fifteen minutes, then washed off. That short-contact design is not incidental — it limits both irritation and the amount of time anyone has to live with the smell. Leaving it on longer or applying it more often than the protocol is not supported by the trials and is the usual route to irritation.

Conflicts & combinations

No documented chemical conflict with common actives. Sunscreen is not optional alongside it, since ultraviolet drives the pigment the product is working against. Because cysteamine is a reducing thiol, putting it in the same application as a strong oxidiser such as benzoyl peroxide is chemically unwise — that is reasoning from the chemistry rather than a trial result, but there is no reason to test it on your own face. Pairing with niacinamide, azelaic acid or tranexamic acid is common in practice, though combination trials are limited.