Why should transformer oil never be used for massage or cosmetic purposes?

Transformer oil is an industrial dielectric fluid, not a cosmetic grade product. It can contain irritants, degradation byproducts, and in legacy cases hazardous contaminants like PCBs. Even non PCB oils are not formulated or tested for skin exposure, inhalation during heating, or microbiological safety. Contact can cause dermatitis and other health effects, and impurities can increase risk. Safe practice is to treat it as a chemical product, follow the SDS, and avoid any personal use.