I recently bought a UV flashlight. I was looking for urine stains on my son’s bedding. In the dirty clothes hamper were some cotton khaki pants. Under UV light they have big stains near the waistline. Under normal light nothing is visibly different. I tied some other pants that I think are also cotton, but see it only in the light colors. Is it something from when the cloth was manufactured?
There’s no telling- it could be any of the dozens of things that glow under UV light.
Why are you searching for urine stains with a UV light? That seems really weird.
Have you used any kind of stain remover other than your regular detergent there?
How old is your son? The answer may differ if he’s 5 vs 14.
Everyone always shines a light on comforters and says “OMG, it’s SEMEN!” But, just for the record, laundry detergent shows up very brightly under a black light as well. In my college is was pretty common to paint the walls (graffiti style) with detergent. Everything looked normal during the day, but at night you’d turn on the black lights and all the writing would show up.
For anyone that plans to take their black light to a hotel and complain about how dirty everything is, they may want to take a look at their own towels and (washed) comforters and clothes first. They might be surprised.
Sweat can flouresce as well- could it be sweat collecting around the waistband of your khakis?
The pants have gone through a wash. Under the UV light the stain looks like someone swiped a paintbrush from wallet pocket to front pocket.
When you wash clothes*, do you put the detergent into the machine, start the water running, and then load the dirty clothes (etter) or do you load the dirty clothes first, and then start the water & add the detergent.
If you do it the latter way, and that pair of pants happened to be the top item in the washer, and the detergetn was poured onto that part of the pants, it might leave such a UV ‘stain’ on the pants.
*Assuming top-load washer here.