Eleven volunteers wore a noninsulated boot on one foot and an insulated rubber boot filled with water on the other foot during 72 hours of immersion in swamps. Both feet were continuously wet, but the temperature of one foot of each man was approximately 20 F (11.2 C) higher than the other throughout the study. Results indicated that symptomatic tropical immersion foot can be produced without any element due to cold injury or heat loss, and that symptoms occurred more rapidly at the higher temperature.
Taplin D, Zaias N, Blank H. The Role of Temperature in Tropical Immersion Foot Syndrome. JAMA. 1967;202(6):546-549. doi:10.1001/jama.1967.03130190152032