There are a number of reasons your socks could be causing rashes, redness, or itchiness on your feet. It could be the material itself (such as polyester), something that's been added (like dye), or the way the socks fit your feet (like if they are bunched up or rubbing). If you're experiencing irritation, try switching to undyed, cotton socks that are the proper fit for you. Removing your socks after working out or sweating a lot may help as well. If you have specific allergies, you might also want to your dermatologist or doctor for recommendations. See this article or more information about clothing allergies.