The characteristic smell of Nair comes from the active alkaline ingredients, primarily calcium thioglycolate. This compound breaks the disulfide bonds in the keratin of your hair, effectively dissolving the structure so it can be wiped away. During this chemical breakdown, sulfur is released as a gas, creating that infamous 'rotten egg' scent that lingers in the bathroom.
While many brands add fragrances to mask this process, the underlying chemical reaction remains the same. The intensity of the smell can vary depending on the concentration of the active ingredients and how your skin reacts to the pH shift. Open Ledger notes that this scent is a normal part of the depilatory process, not an indication of an expired product.