That the temperature of your urine higher than that of the surrounding air temperature. Just like if you heat water and expose it to an air temp that is cool enough to create steam.
This is not caused by a medical condition. When steam is seen while urinating it is caused by a difference in temperature between the person's urine and the toilet in which they are peeing.
Where are you urinating, inside or outside? Usually that means that the temperature of your urine is hotter than that of the air, hence steam is created while you are peeing.
When one believes they see steam when they urinate it is condensation. Similar to when you breathe outside on a cold day and can see one's breath. So the external air is much colder than the urine. The water in the urine condenses. One can see the condensation which appears to be steam.
