I have redness and soreness at the base of the nail on both big toes. What could be causing this?

Alot of things can happen to our big toes and there are quite a few things that could cause this. Injury can - but thats probably unlikely since both of your big toes are affected.  Other possibilities include gout, arthritis, a bunion or a fungal infection. You might want to check out the Check a Symptom box in the upper left-hand corner of the page to see if you can narrow down the possibilities but you'll probably have to see a physician to find out what's going on.

Gout usually occurs in men and women over 40 and bunions are more common in women who wear poor fitting shoes.

Heres some information on gout: http://www.healthcentral.com/encyclopedia/408/174.html

And here's some information on bunions:

http://www.healthcentral.com/encyclopedia/408/467.html

It could also be paranychia, or ingrown toenails.Ingrown toenails being less likely since it is bilaterally. I would suggest that you go for a visit to a podiatrist, to rule out gout.