Isobutylamido Thiazolyl Resorcinol

Isobutylamido Thiazolyl Resorcinol (aka Thiamidol, made by Beiersdorf and used in Eucerin products) is a brightening ingredient that targets uneven skin tone, dark spots, and hyperpigmentation.

It works by blocking tyrosinase, the enzyme responsible for melanin production, so less pigment is deposited into your skin.

What makes it stand out is how specific it is to human tyrosinase: it was discovered by screening more than 50,000 compounds against recombinant human tyrosinase rather than the mushroom version most older ingredients were tested on.

Thiamidol turned out to be superior to frequently used inhibitors of hyperpigmentation (kojic acid, arbutin, and even hydroquinone) in lab testing.

The clinical evidence is solid as well for a cosmetic ingredient; it matched or beat a 2% hyroquinone for mild-to-moderate melasma in a double-blind study, reduced visible age spots at concentrations as low as 0.1% within 4 weeks, and separate trials show it helps with post-inflammatory hyperpigmentation (the marks left behind after acne).

This ingredient is generally well-tolerated since it doesn't rely on the quinone-forming mechanism that can irritate skin. Studies also report minimal and self-limiting side effects.

Typical usage concentration in finished products is 0.2% (the same amount most of the clinical trials used) and it shows activity as low as 0.1%.

Overall, this is a better-researched brightening active and is a great option if pigmentation is your concern.

Be sure to also check out Rucinol, another "hydroquinone alternative".