What would cause excessive foot sweating with no prior history?

I would be looking for a systemic cause for example overactive thyroid , new medications, increased intake of caffeine, fever from infection which may not be obvious such as a urine infection or low grade fevers from other less common causes Please see your physician to rule these out .Treating the symptom is possible with botox if no underlying cause is found however it takes a lot of product , requires anaesthesia and is generally not as effective as treatment for underarm or hand hyperhydrosis

It is unlikely that you have an underlying medical problem if you have isolated sweating from the feet. Nevertheless, the only test you need in most cases is a thyroid function test which will most likley be normal. If it were a generalized health problem, you would sweat from many places in the body. Plantar hyperhidrosis is common and perhas you had cold damp feet and hands and now the condition has worsened and now you have obvious sweating. Read the ebooks about palmoplantar hyperhidrosis on the link below.