Generally, submerging your head in hot water is a bad idea—especially somewhere communal.
Water between 102 and 104 degrees Fahrenheit breeds bacteria, a reason why hot tubs require sanitation. Thankfully, bathing your legs or torso in the water does not fully expose you to these potential bacteria.
However, your nose, eyes, ears and mouth give easy ingress to your body, meaning you are more likely to catch an illness or infection with your head underwater.
Even in perfectly clean water, high temperatures pose a hazard to children’s brains. While children should not enter a hot tub above 95-or-so degrees anyway, those who do are at a greater risk of hindering brain development when getting their heads wet. A child’s body is more sensitive to heat and cannot regulate its temperature as effectively. The head, specifically, is vulnerable to overheating because it is a major source of heat loss.
For both adults and children, the jets in a hot tub introduce yet another danger. When you dunk your head underwater, you risk catching your hair in the jets and filters. Regardless of how shallow the spa, if your hair gets caught you might not be able to surface for air. Thus, we recommend wearing a bathing cap if you have long hair.
For advice on buying a hot tub please read The Ultimate Hot Tub Buyers Guide.