Biologists have proven that looking at women constantly stimulates man's sexual desires and hormones which in time weakens the immune system and causes many diseases. Researchers say that the best remedy for this problem is to avoid sexual looks at women. Prophet Mohammad, PBUH, solved this problem at its roots when he told Ali Ibn Abu Talib, may Allah be pleased with him, "Oh Ali, don't make the first look be followed with another look for the first is yours but the second isn't." narrated by Tirmidhi. All glory to Allah.

Allah the almighty says:

*"Tell the believing men that they should reduce/lower their gaze/vision and guard their private parts" (Quran:24:30)

*"Tell the believing women that they should reduce/lower their gaze/vision and guard their private parts" (Quran 24:31)

Source ; http://www.recoveryranch.com/articles/sex-addiction/pornography-addiction/