but what is tretinoin exactly? It’s a prescription-only retinoid that’s commonly referred to as tret, Retin-A, or Altreno, explains board-certified dermatologist Pooja Rambhia, M.D. FAAD.

There are several different Rx brands of tretinoin that dermatologists prescribe; Altreno and Retin-A are two of the most popular, but it’s also common to receive the generic version.

Celebrities such as Hailey Bieber are swearing by a secret ingredient, a retinol alternative called tretinoin (pronounced tret-in-oh-in), aka retinoic acid, which, if you’re not all over TikTok ...