The amount of chemical it takes to harm your health will depend on what that chemical is. While some chemicals are known to be highly toxic, like mercury compounds or cyanogen gas where even exposure to a small amount can be deadly, other chemicals become harmful with very high or accumulated exposures. The most common route is through inhalation. We breathe in or inhale chemicals, along with air, as vapour mists, fumes, gases, fibers or dust. Some toxic chemicals like ammonia and sulfuric acids can burn the airways and the throat in the process.
Skin contact is another method.
Some chemicals are able to get through the protective outer layer of our skin or they can stick to body hair and enter through the hair follicles. This is important to know when you are working with certain pesticides and some solvents. Finally in distant third place, chemicals can enter our bodies through the digestive system. Eating or swallowing chemicals in the workplace is unusual, yet traces of a chemical can transfer from your fingers on to your food, or cigarettes and then enter your body when you eat or the cigarette touches your lips. First of all, know the chemical.