The blackness in front of your eyes when you take a shower and faint may be caused by the lack of blood and oxygen in the brain. When taking a bath, the general indoor air circulation is poor, and the indoor temperature is high, which may easily cause the brain to lack oxygen. In addition, the water is generally hotter when taking a bath, which can easily cause severe overexpansion of blood vessels, and the expansion may cause impaired blood supply to the brain. In addition, the bath may also cause hypovolemia due to the large amount of sweating, and severe hypovolemia may cause cerebral hypoperfusion, which may easily cause cerebral hypoperfusion. In case of insufficient blood supply to the cerebellar brainstem, the patient usually presents with dizziness, balance disorders and ataxia. When the cerebral blood supply is insufficient, the patient can have blackness in front of the eyes, and can also have limb sensory impairment and motor dysfunction, so the bath must be promptly ventilated indoors and given more water if necessary to replenish the blood volume, and at the same time, the bath water must not be too hot when bathing.