Most bumps on the eyelid are styes. A stye is an inflamed oil gland on the edge of your eyelid, where the lash meets the lid. It appears as a red, swollen bump that looks like a pimple. It is tender, especially to the touch.

A stye is caused by bacteria from the skin that get into the oil glands in the eylids that provide lubrication to the tear film. Styes are similar to common acne pimples that occur elsewhere on the skin. You may have more than one stye at the same time.

Styes usually develop over a few days and may drain and heal on their own. A stye can become a chalazion -- this is when an inflamed oil gland becomes fully blocked. If a chalazion gets large enough, it can cause trouble with your vision.

If you have blepharitis (see eye redness), you are more likely to get styes.

Other possible eyelid bumps include:

• Xanthelasma -- raised yellow patches on your eyelids that can happen with age. These are harmless, although they are occasionally a sign of high cholesterol.
• Papillomas -- pink or skin-colored bumps. They are harmless, but can slowly grow, affect your vision, or bother you for cosmetic reasons. If so, they can be surgically removed.
• Cysts -- small fluid-filled sacs that can affect your vision.

In addition to the red, swollen bump, other possible symptoms include:

• Tearing of your eye
• A gritty, scratchy sensation as if there is a foreign body
• Sensitivity to light
• Tenderness of the eyelid

A doctor can diagnose a stye just by looking at it. Special tests are usually not necessary.