Bay rum is a type of cologne/aftershave lotion. Other uses include as under-arm deodorant and as a fragrance for shaving soap, as well as a general astringent.
It is a distillate that was originally made in Saint Thomas "and probably other West Indian islands" from rum and the leaves and/or berries of the West Indian bay tree, Pimenta racemosa.
John Maisch identified the leaf in the herbarium at the Philadelphia Academy of Natural Sciences, collected in St Croix, "by the late Dr, Griffith", which was identified as Myrcia acris, now transferred to the genus Pimenta. Maisch added that it was "very probable that various species are made use of for the same purpose." Other ingredients may be citrus and spice oils, the most common being lime oil, oil of cloves. A drop of oil of cloves is added to two parts bay oil and one part pimento oil in one of two recipes for bay rum; the aromatics are steeped in alcohol and as a last step an equal part of "good rum" is added, and cinnamon.
It was first made fashionable in New York and other American cities before it was available in Europe. This Rexall bay rum example (pictured) from the Prohibition era in the United States was labeled "for external use only", but with 58% grain alcohol it was often used as a legal, if somewhat toxic, source of beverage alcohol.