Lead acetate cotton is primarily used in forensic science for the detection of hydrogen sulfide gas. When exposed to air containing hydrogen sulfide, the cotton undergoes a chemical reaction that results in a color change, typically turning black. This makes it a useful tool in identifying the presence of hydrogen sulfide in various environments, such as in industrial settings or during environmental monitoring. Additionally, it has been historically used in some cosmetic applications, particularly in hair dyes, although its use in such products has significantly declined due to safety concerns.