Treat sunburn to the feet by getting out of the sun, taking a cool shower, applying a cooling agent and taking an over-the-counter pain reliever, according to About.com. In some cases, swelling of the feet due to sunburn is a medical emergency. If the swelling completely circles the feet causing them to become numb, tingly, blue or cold or they feel like they have "fallen asleep," seek immediate medical attention.
Look for blisters on badly burnt feet as they can be an indication of complications, according to About.com. If blistering does occur and covers the entire foot or both feet, seek medical attention to treat the skin. Soak feet in cool water periodically to obtain relief and help alleviate some of the swelling. Use a cooling agent, such as aloe or a commercially prepared sunburn relief cream, to ease the pain and heat associated with a bad burn. Avoid applying any type of oil to the burnt skin until swelling and pain subsides.
Using sunscreen before sun exposure is the best way to prevent sunburns and the associated swelling. Once the skin is already burnt, it is just as important to stay out of the sun to prevent further aggravation to the skin. Wear loose-fitting light cotton socks, if necessary, while the burn is healing to prevent aggravating the skin.