Why does alum work on blisters in the mouth/cold sores?
Alum has been shown to be effective in treating aphthous stomatitis (canker sores) and it is believed to be due to the compound's significant drying effect. Alum is known as an astringent - a chemical compound that tends to shrink or constrict body tissues. More information on alum's astringent properties are reported in this paper. As the infected tissue shrinks there is a decrease in pressure due to swelling and this less pressure around the nerves in the affected area. The exact mechanism is still under question.