Treato found 16 discussions about Cold Symptoms and Cats Allergy on the web.
Best Answer: When the toilet is flushed, the toilet is robbing pressure from the shower, which is usually close to the toilet. As the COLD water pressure goes down from the toilet flush, the HOT water pressure is higher, therefore the water gets hotter as the COLD pressure goes down.
Sounds to me like high humidity. When your bathroom gets hot and the water condenses it will start to run down the walls. If you have a fan, turn it on while the hot water is running. It should take care of the problem. You might also wipe down the walls after a shower.