While many products are conditioners that improve the health of lashes enabling them to be their natural best (ie coconut oil) , the active ingredient in lash growth serums is Prostaglandin (PG). These hormone-like substances participate in a wide range of body functions such as the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels, control of blood pressure, and modulation of inflammation. Latisse is actually a mainstay in the treatment of glaucoma, a disease of the eye. Somewhere along the line it was discovered that there was a happy side effect to this treatment: it made eyelashes grow like weeds.
PG's extend the growth cycle of the lash follicle and it is believed they increase the percentage of active follicles. Although prescription serums have higher concentrations of the most effective Prostaglandins, the majority of high end over the counter products also contain the protein.
There are common side effects to using these serums that are worth considering:
Unwanted hair growth in areas the product repeatedly touches
Darkening of the eyelids
Permanently increased iris pigmentation, which could irreversibly turn light eyes brown, especially if your irises are hazel or green
Read more:
https://aestheticsjournal.com/feature/eyelash-and-eyebrow-growth