Eye black is a substance, either a grease or a strip, that is applied under the eyes to reduce glare. It is commonly used by athletes in sports such as American football, baseball, and softball. The glare reduction is important because when a player is running across a field, there are many bright lights pointed in their direction, from the stadium lighting to the direct sunlight. This light can impede their depth perception and ability to catch the ball as it flies through the air. Eye black is thought to work by reducing the amount of glare that reaches the eyes. Because black colors absorb most light frequencies, it is thought that the excessive light coming from sources we are not looking at will be absorbed by the black color. Placing the black just below the eyes will, in effect, reduce the glare, thereby increasing the definition and contrast of the objects we are looking at.

Studies have been conducted to determine the effectiveness of eye black, and while there is some disagreement among experts, most studies have found that it does reduce glare and improve contrast sensitivity. One study found that eye black grease made of beeswax and pigment was more effective than anti-glare stickers. However, researchers are still unsure how much impact the glare reduction and contrast improvement translates into an “on-the-field” advantage for athletes.