Gums are considered to be one of the most stained oral tissues in the body. Darkening of the gums is actually a form of gingival hyperpigmentation. Both endogenous and exogenous causes can lead to darkening of the gums. It can range from physiological causes to systemic diseases and medication use. Physiological hyperpigmentation presents clinically as multifocal or diffuse melanosis and has a variable prevalence in different ethnic groups. It is common in African, Asian and Mediterranean populations and is due to greater melanocyte activity rather than more melanocytes. The gums are the most common site of this hyperpigmentation. No specific treatment is usually required. Many pathological causes can also lead to darkening of the gums. Some of the more common ones are excessive exposure to heavy metals in the body. Lead, bismuth, mercury, silver, arsenic and gold. In children, possible sources of exposure include lead-contaminated water or paint and medications containing mercury or mercury-containing drugs. Pigmentation appears as a blue or black line along the gingival margin and is proportional to the amount of gingival pigmentation. The importance of oral mucosal hyperpigmentation associated with heavy metals lies primarily in identifying and treating the underlying cause to avoid serious systemic toxic effects. A variety of drugs including chloroquine, quinine, minocycline, zidovudine, chlorpromazine, ketoconazole, bleomycin, and cyclophosphamide are known to cause melanosis. It may involve the accumulation of melanin under the influence of drugs or iron deposition after dermal damage. The darkening of the gums caused by these drugs can gradually improve after stopping the use of the drugs. There are many causes of gum darkening, some of which are reversible in nature, while others require aggressive treatment to address the cause.