Anything that removes hair can be called a depilatory. Hair removal creams are known as chemical depilatories because that's how they eliminate hair -- with alkaline chemicals, such as sodium thioglycolate, strontium sulfide and calcium thioglycolate.
Once they come in contact with your skin, these chemicals smash the protein bonds that hold your hair together. Afterward, these proteins, known as keratins, are so weak that hair falls from the follicle. The end product is something like jelly that can be rubbed off [source: Cressy].
If you're wondering why hair removal creams can smell so awful, here's your explanation: a chemical reaction between calcium thioglycolate and sodium hydroxide. It's possible to find products with scents to cover up the sulfuric odor, but remember that additional ingredients can be irritants.