Reverse smoking is common in:

Reverse chutta (crude form of cigar) smoking, practised especially among females of Srikakulam district of Andhra Pradesh, recorded a prevalence of 8.8% of leukoplakia, 4.6% preleukoplakia and 17.9% leukokeratosis nicotina palati (Daftary et al, 1992). Palatal involvement was noted in 85% of the leukoplakia cases and in 57% of the preleukoplakias, and, of course, in all of the cases of Ieukokeratosis nicotina palati. Palatal changes associated with reverse smoking thus exhibited a spectrum of clinical changes, and it was not satisfactory to group them under leukoplakia, preleukoplakia or leukokeratosis nicotina palati. Reference: Shafer’s Textbook of ORAL PATHOLOGY Eighth Edition page no 145