A sty is a red, painful lump near the edge of your eyelid that may look like a boil or a pimple. Sties are often filled with pus. A sty usually forms on the outside of your eyelid. But sometimes it can form on the inner part of your eyelid.

In most cases, a sty will begin to disappear on its own in a couple days. In the meantime, you may be able to relieve the pain or discomfort of a sty by applying a warm washcloth to your eyelid.

Source: http://www.mayoclinic.com

Signs and symptoms of a sty include:

• A red lump on your eyelid that is similar to a boil or a pimple
• Eyelid pain
• Eyelid swelling
• Tearing

Another condition that causes inflammation of the eyelid is a chalazion. A chalazion occurs when there's a blockage in one of the small oil glands at the margin of the eyelid, just behind the eyelashes. Unlike a sty, a chalazion usually isn't painful and tends to be most prominent on the inner side of the eyelid. Treatment for both conditions is similar.

When to see a doctor

Most sties are harmless to your eye and won't affect your ability to see clearly. Try self-care measures first, such as applying a warm washcloth to your closed eyelid for 5 to 10 minutes several times a day and gently massaging the eyelid. Contact your doctor if:

• The sty doesn't start to improve after 48 hours
• Redness and swelling extend beyond your eyelid and involve your cheek or other parts of your face

Source: http://www.mayoclinic.com

A sty is caused by an infection of oil glands in the eyelid. The bacterium staphylococcus is responsible for most of these infections.

Source: http://www.mayoclinic.com

Your doctor will usually diagnose a sty just by looking at your eyelid. Your doctor may use a light and a magnifying device to examine your eyelid.

Source: http://www.mayoclinic.com

To prevent eye infections:

• Wash your hands. Wash your hands with soap and warm water or use an alcohol-based hand sanitizer several times each day. Keep your hands away from your eyes.
• Take care with cosmetics. Reduce your risk of recurrent eye infections by throwing away old cosmetics. Don't share your cosmetics with others. Don't wear eye makeup overnight.
• Make sure your contact lenses are clean. If you wear contact lenses, wash your hands thoroughly before handling your contacts and follow your doctor's advice on disinfecting them.
• Apply warm compresses. If you've had a sty before, using a compress regularly may help prevent it from coming back.
• Manage blepharitis. If you have blepharitis, follow your doctor's instructions for caring for your eyes.

Source: http://www.mayoclinic.com

Until your sty goes away on its own, try to:

• Leave the sty alone. Don't try to pop the sty or squeeze the pus from a sty. Doing so can cause the infection to spread.
• Clean your eyelid. Gently wash the affected eyelid with mild soap and water.
• Place a warm washcloth over your closed eye. To relieve pain, run warm water over a clean washcloth. Wring out the washcloth and place it over your closed eye. Re-wet the washcloth when it loses heat. Continue this for 5 to 10 minutes. Then gently massage the eyelid. Repeating this two to three times a day may encourage the sty to drain on its own.
• Keep your eye clean. Don't wear eye makeup until the sty has healed.
• Go without contacts lenses. Contact lenses can be contaminated with bacteria associated with a sty. If you wear contacts, try to go without them until your sty goes away.

Source: http://www.mayoclinic.com

You are at increased risk of a sty if you:

• Touch your eyes with unwashed hands
• Insert your contact lenses without thoroughly disinfecting them or washing your hands first
• Leave on eye makeup overnight
• Use old or expired cosmetics
• Have blepharitis, a chronic inflammation along the edge of the eyelid
• Have rosacea, a skin condition characterized by facial redness

Source: http://www.mayoclinic.com