A fuel cell uses a chemical reaction between hydrogen and oxygen to produce electricity.
Realizing that the total weight of all the products of a chemical reaction must be exactly equal to the total weight of the reacting substances, he made the balance the ultima ratio of the laboratory, and he was able to draw correct inferences from his weighings because, unlike many of the phlogistonists, he looked upon heat as imponderable.
When you compare the DHA chemical reaction to the possibility of skin cancer from the sun, a spray tan sounds like a much safer tanning option.
The result of the chemical reaction is the overall good feeling that envelopes your body after a massage.
This causes a chemical reaction resulting in the spray foam you see.