Why might confusion occur in an elderly person taking a hot bath?

Only when bathing?: I'm not aware of anything medical to explain why anyone, regardless of age, would become confused only when taking a hot bath, assuming that they don't become confused using more tepid water or when not bathing. My guess is that there's an underlying condition, perhaps dementia, that's exacerbated by misunderstanding or fear of bathing. Try a bird bath instead. You know, sponge bath. Or shower.