Like other astringents, it has been recommended in agues and haemorrhages, and is a good substitute for Quinine in intermittent fever, especially when given with Chamomile flowers.
It is useful in chronic diarrhoea and dysentery, either alone or in conjunction with aromatics. A decoction is made from 1 OZ. of bark in a quart of water, boiled down to a pint and taken in wineglassful doses. Externally, this decoction has been advantageously employed as a gargle in chronic sore throat with relaxed uvula, and also as a fomentation. It is also serviceable as an injection for leucorrhoea, and applied locally to bleeding gums and piles.
Externally it can be used to treat hemorrhoids, inflamed gums, wounds, and eczema. The tannin found in oak can help reduce minor blistering by boiling a piece of the bark in a small amount of water until a strong solution is reached, and applying to the affected area.
To cure frostbite, American folk medicine called for collecting oak leaves that had remained on the tree all through the winter. These leaves were boiled to obtain a solution in which the frostbitten extremities would soak for an hour each day for a week.
From: A Modern Herbal