Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans.

Why are thiols important?

Thiols are a type of mercaptan characterized by having a sulfhydryl functional group. Biothiols (or biologically derived thiols) are the most important antioxidants that protect cells from any kind of oxidative damage (5, 6).

What is an example of a thiol?

A thiol generally has a much lower boiling point than the hydroxyl compound of like structure; for example, methanethiol boils at 6° C (43° F), methanol at 65° C (149° F). The lower aliphatic thiols are useful as warning odorants in fuel gases and are somewhat toxic.