The look is one of the poisonous arrows of the Devil. If a person shoots it out, it is indeed a poisonous missile that kills the one who sends it. This arrow returns back to the heart of the one looking.

The look is a poisonous arrow that returns to the heart of the onlooker, striking it and affecting it, or killing it and causing it to die. So none of them should look at what Allaah has forbidden. The creation of this look and this eyesight is a blessing, which humans must use for only that which Allaah has permitted. He must use them for only those things that Allaah has allowed and refrain from using them for those things that Allaah has forbidden. Allaah says about men: “Tell the believing men to lower their gaze.” [Surah An-Noor: 30] And He says about women: “And tell the believing women to lower their gaze.” [Surah An-Noor: 31]

Source: Advice to the Muslim Woman – Shaykh Saalih bin Fawzaan al-Fawzaan [Book]