Different Hygiene
Credit: Getty Images

Many kinds and levels of substance use can be ferreted out with this observation. People who smoke cigarettes may try to cover it up with cologne or mouthwash. Eye drops may be used to sooth red eyes. These habits aren't necessarily cause for alarm. However, Compton says serious deteriorations in hygiene – lack of showering or unclean clothes – can be a very strong indicator of extreme substance use.