Both corns and calluses are thickened and hardened patches of skin caused by friction and pressure.
Corns have a hard, cone-shaped core that points inward, often pressing on a nerve and causing pain. They usually appear not only on the tops, sides, and tips of toes but also on the soles of the feet, on the ball (over the metatarsal arch). When they appear between toes (usually between the 4th and 5th toes), they are called soft corns and they look whitish in appearance, because of the dampness from perspiration. Some corns occur under a callus.
Calluses are more diffuse thickenings of the skin that usually develop on the palms of the hands and the soles of the feet, especially underneath the bottom ends of the foot bones.
Friction and pressure cause both corns and calluses. In the case of corns, the pressure is typically caused by tight-fitting shoes or high heels, or even tight-fitting stockings or socks. But be aware: corns often don't appear at sites of obvious pressure.
Tight shoes also cause calluses to grow on the feet where extra pressure is exerted on different parts of the feet, often because of an uneven gait, or a bunion (a bony bump on the joint at the base of a big toe), a hammertoe (a toe that is clenched like a claw), a bone spur, or other foot deformities.
Calluses also frequently grow on the hands from using tools or instruments without wearing gloves. Different types of calluses include hand calluses (from using a shovel), writer's callus (from holding a pen or pencil), and finger calluses (from playing the guitar).
Corns and calluses can become inflamed or develop ulcers. If this happens, consult your doctor.
Once you know what to look for, it's usually easy to tell whether you have a corn or a callus. If you are concerned about its appearance or it becomes inflamed or more painful than usual, check with your doctor, who will rule out other causes of thickened skin, such as warts and cysts. Your doctor may also request an X-ray to see if a physical abnormality is causing it.
Wear only proper fitting shoes, with plenty of room to wiggle your toes but not so big that your feet slide forward. If you are prone to corns, consider cushioned shoe inserts to absorb the shock, and avoid tight-fitting socks and stockings. Wear work gloves when using tools to prevent calluses growing on your hand. In many cases, however, calluses are unavoidable (you can't wear gloves to play acoustic guitar!); they're part of the normal wear and tear of life.
Most corns can be self-treated by removing the source of the pressure and letting the skin heal on its own. If your corn is caused by an ill-fitting shoe, replace your shoes with ones that fit properly. Consider wearing a donut-shaped corn cushion (available at your local pharmacy) to protect the corn as it heals. After bathing, you can rub away corns or calluses with a pumice stone or washcloth. If you remove tough skin regularly in this fashion, the skin won't get a chance to become callused. No "bathtub surgery"; cutting or paring away corns or calluses yourself can lead to infection.
Consult your pharmacist before buying any over-the-counter liquid corn remover or medicated corn pads. Salicylic acid is the active ingredient in these products. It eats away the thickened skin and any other skin it comes into contact with. In general, they aren't necessary and can be dangerous if you are diabetic or have poor circulation.