Individuals who sweat excessively experience what is known as hyperhidrosis. They frequently try anti-perspirants and often find that these do not adequately control their sweating.
Most over-the-counter anti-perspirants contain a low concentration of aluminum chloride. Aluminum chloride works by blocking the pore out of which sweat comes, minimizing sweating. Less sweat means less moisture in which bacteria can grow and this in turn leads to less odour. The term "deodorant" strictly refers to products that mask odour, often using fragrances. These do not control sweating and tend to be less effective. Most over-the-counter products contain both the anti-perspirant ingredient aluminum chloride as well as fragrances.
For individuals who sweat excessively and for whom over-the-counter anti-perspirants do not control sweat or odour, a number of options exist. These are described in detail here. The best place to start is usually with an over-the-counter product that contains a higher concentration of aluminum chloride (typically 6-20%). These are often effective but can be irritating to the skin.
If topical treatments are ineffective or are not well-tolerated, the problematic areas can be treated with injections of botulinum toxin. This frequently reduces sweating by up to 90% and tends to have a dramatic effect on individuals' quality of life.
Other treatment options include oral medications that suppress sweating and surgery. The latter is usually used as a last resort as it is more invasive. If you suffer from excessive sweating (also known as hyperhidrosis), consider seeing a dermatologist to review your options.