[7][8] Various esters of phorbol have important biological properties, the most notable of which is the capacity to act as tumor promoters through activation of protein kinase C.[9] They mimic diacylglycerols, glycerol derivatives in which two hydroxyl groups have reacted with fatty acids to form esters.

The most common and potent phorbol ester is 12-O-tetradecanoylphorbol-13-acetate (TPA), also called phorbol-12-myristate-13-acetate (PMA), which is used as a biomedical research tool in contexts such as models of carcinogenesis.

[10][11] Phorbol is the active constituent of the highly toxic New World tropical manchineel or beach apple, Hippomane mancinella.

In the manchineel, this leads to an additional exposure risk during rain, where liquid splashing from an undamaged tree may also be injurious.

When phorbol esters bind to the receptor, they are not degraded as efficiently by the body, leading to constitutively active PK.

[16] Previously, the difficulty with synthesizing phorbol had been creating C–C bonds, especially in the six-membered ring at the top of the molecule.

[citation needed] The phorbol ester tigilanol tiglate reportedly has in vitro anti-cancer, antiviral, and antibacterial activities.

[10] The phorbol derivatives in croton oil are used in folk medicine, with purported purgative, counter-irritant, or anthelmintic activities.