Antiperspirant deodorants often claim to offer "24-hour" protection. What determines the length of time a deodorant works and how do they test for it? How does the chemical composition of the deodorant prevent perspiration?

Rowan Howell Lewes, East Sussex, UK

3 of us tried to quit smoking while working at a typewriter repair shop where we used strong chemicals to clean the machines. For some reason the smell of the chemicals made us laugh uncontrollably. Only while we we're trying to quit. None of us ended up quiting and when we started smoking again, no more laughing like crazy Why did that happen?