Oral cancer in India is most strongly associated with tobacco, whether smoked as cigarettes and bidis or chewed in the form of gutkha, khaini, paan masala and betel quid.

Tobacco contains carcinogens such as tobacco-specific nitrosamines that, on repeated contact with the lining of the mouth, damage the DNA of oral cells and trigger uncontrolled malignant growth.

Soft drinks, fried food and a high-salt diet carry other health risks but are not the recognised primary cause of oral cancer, which is why India's high rate of the disease is linked chiefly to chewing and smoking tobacco.

Hence, the substance strongly linked to oral cancer in India is tobacco.