Danger: Mana Poisoning
One thing often not considered with magic is that generally, the body of a bog-standard human isn't capable of dealing with the raw concentrations of mana that comprise spells. Thus ether, being condensed, highly-concentrated magic, is likely to produce mutagenic effects in those exposed to it.
Depending on the method and time frame of exposure, this can range from cancerous, radiation poisoning sickness from long-term evaporation, all the way to explosive tentacular growth for heavy physical saturation.
As a tool, ether has many uses and much utility, but it also presents very real dangers, especially for those who are exposed to it for long periods.