These woman’s teeth are stained red because of the betel nut. An ancient practice, the betel nut is wrapped in a betel leaf along with white lime and other ingredients such as clove or cardamom. Sometimes tobacco is included contributing to the additive nature of the mix. 

It is presented in a precious little green package meant to be placed in the mouth, chewed until the red juice flows, and then spit with gusto onto the ground.  Men and women alike indulge. The betel hut is dangerous however and can cause cancer. (Source)