Chilblains - Wikipedia are typically caused by too rapid heating of cold toes, whether induced by environmental cold or by poor circulation.
Cold feet put into warm water can feel painful, like they are in scalding water. Cold toes especially can have very poor circulation (to preserve body heat).
When toes are exposed to heat, such as warm water, their blood vessels dilate and allow blood to flow more freely. Unfortunately they can heat unevenly, and some parts of a toe will suddenly have free flowing blood while other parts are still constricted. This unbalanced situation can cause physical damage to the blood vessels, known as chilblains, with symptoms similar to first and second degree burns.
Having a drink of alcohol before taking a bath or shower is an effective method of helping to prevent this damage. The alcohol increases the circulation throughout the body by dilating the blood vessels. A few minutes after a drink, one's toes will have already regained full circulation and become warm. So when they eventually do encounter the warm bath water, chilblains can't happen.
But continual use of alcohol, even when literally taken "for medicinal purposes", isn't necessarily a good idea.
Are there other vasodilators (or other treatments) that can be used for the same purpose that don't have potentially harmful side-effects?