Sudden or long-term immersion in a tub of hot water can heat the body and put stress on the heart, explains Cleveland Clinic. This poses a risk to individuals with existing heart disease. Exposure to hot baths and hot tubs can also cause male infertility, though the effects are potentially reversible, notes the University of California, San Francisco. During pregnancy, water that is too hot potentially causes harm to a developing baby, reports BabyCenter.
When a person submerges himself in hot water, his heart rate increases and his blood pressure drops, reports Cleveland Clinic. Sweating cools a person's body down, but the sweating mechanism does not work when an individual is submerged in hot water. This is problematic for individuals with existing heart conditions and may cause a loss of sufficient blood pressure, a heart attack, nausea, dizziness or abnormal heart rhythms. An individual with cardiovascular disease may also experience inadequate blood flow to the heart or body or an increase in blood pressure if his body becomes superheated.
A study led by a urologist from the University of California, San Francisco, found that when a male's body undergoes total exposure to wet heat, it impairs sperm production and motility. The study also concluded that this effect was reversible in almost half of the males who stopped submerging themselves in wet heat, explains the University of California, San Francisco.
Water above 100 degrees Fahrenheit can cause a pregnant woman to overheat, reducing blood flow to the developing fetus and raising the mother's heart rate, states BabyCenter. This can interrupt a baby's normal development or put stress on the baby. It is also more likely for a pregnant woman to pass out upon becoming overheated, as it is more difficult for a woman's body to cool down during pregnancy.