Traces of chloroform is also formed in swimming pools that are disinfected with chlorine or hypochlorite in the haloform reaction with organic substances (e.g. urine, sweat, hair and skin particles). Although it is possible to inhale THMs, the U.S. EPA has determined that this exposure is minimal compared to that from consumption. In swimmers, uptake of THMs is greatest via the skin with dermal absorption accounting for 80% of THM uptake. Exercising in a chlorinated pool increases the toxicity of a "safe" chlorinated pool atmosphere with toxic effects of chlorine byproducts greater in young swimmers than older swimmers.