Cold application with friction rub after heat therapy is believed to work by causing vasoconstriction, which locks heat in and facilitates leukocyte demargination, thereby jumpstarting the innate immune system.

“When we look at the data and we try to see why they would do this, we believe that this seems to work because the cold causes vasoconstriction and it locks the heat in. So after you're done, it's not easy for the heat to dissipate through those vasodilated vasculature. But the other thing that it does is, just like we know when you take a cold shower, that vasoconstriction causes demargination of leukocytes, and that causes the amount of leukocytes in the solution if you will, or in the vasculature to go through, find the viral particles and report to their lymph nodes through that increased circulation. And that sort of jumpstarts the innate immune system in finding those epitopes and presenting them to the antigen-presenting cells.”