Latanoprost, Bimatoprost, Travoprost and Tafluprost are active ingredients used in the form of eye drops to lower intraocular pressure in glaucoma patients. Just like the natural prostaglandins, which are their equivalents occurring in the body, the synthetic prostaglandins also bind to the prostaglandin receptors of the cells. Thus, the artificial tissue hormones intervene in the communication between cells in body tissues and can have very different effects depending on the place of application.
When applied in the eye, Latanoprost and Bimatoprost expand the drainage channels for the aqueous humor (the fluid that fills the front part of the eye) and thus normalize increased intraocular pressure. Their hair-growth-promoting effect has once again been discovered as a side effect: Glaucoma patients who regularly use Latanoprost (trade name Xalatan, among others), Bimatoprost (trade name Lumigan, among others) or other prostaglandin analogues to lower intraocular pressure can often enjoy increased eyelash growth and consequently longer, thicker eyelashes.
In 2008, bimatoprost was approved in the USA under the trade name Latisse as a prescription drug against impaired eyelash growth (hypotrichosis); within a short time, the number of hypotrichosis “diagnoses” shot up. In Europe, bimatoprost or latanoprost are still only used for glaucoma treatment.
However, there are several other prostaglandin analogues which are only approved for cosmetic purposes and apparently are no less effective and are used by cosmetic manufacturers in so-called eyelash serums. These include the substances methylamido-dihydro-noralfaprostal (MDN), dechloro-dihydroxy-difluoro-ethylcloprostenolamide and isopropyl-cloprostenate. In contrast to what one is used to from many cosmetics, the prostaglandin-containing eyelash serums actually do something: regularly applied, the gels which are to be applied once a day on the edge of the eyelid reliably provide very clearly perceptible effects in terms of growth, thickening and darkening of the lashes.
These effects are based on an extension of the anagen phase of the lash follicles. Like Minoxidil, eyelash serums must be applied regularly to maintain the new status quo. When the application is finished, the lashes return to their original state over time. Initially, after discontinuing the product, there may even be increased loss; the new lashes then grow shorter and less thick.
Eyelash serums are not free of side effects: It is not uncommon for reddened, itchy and burning eyes, inflammation of the conjunctiva and eyelid margin, cosmetically unpleasant darkening of the skin around the eyes, temporary visual disturbances and sometimes permanent discoloration of the iris. Occasionally even retinal bleeding, choroidal inflammation and macular edema – quite serious side effects inside the eye – are observed.
Actually, cosmetics with prostaglandin analogues are rather pharmaceuticals: they interfere quite extensively with body processes. It cannot be excluded that one day the German legislator will subject prostaglandin-containing eyelash sera to a closer examination and will prohibit the application for purely cosmetic purposes with reference to the side effects. There is corresponding criticism, for example from the Federal Institute for Risk Assessment ; however, the discussion has been going on since 2011 and has not yet yielded any results.
Prostaglandin analogues in experimental clinical use
There are several small studies on the use of prostaglandin analogs to promote eyelash growth in circular hair loss (Alopecia areata). Their results are mixed – they range from “completely ineffective”  to “well or moderately effective in a total of 45% of patients” . An explanation for such different results is still pending.
Prostaglandin analogues have also been used with some success in studies to treat the scalp in alopecia areata and androgenetic alopecia ; a review article from 2017 suggests that bimatoprost will be the third drug after minoxidil and finasteride that could be approved by the American medical authority FDA for the treatment of hair loss .