Is looking at breasts haram?

Permissibility of Looking at Certain Body Parts

In general, the prevailing opinion, which we also support, is that it is acceptable for a man to observe the visible body parts of his mahram (women he can never marry) such as their faces and limbs. However, it is not permissible for him to gaze at their breasts or to touch them, as this remains forbidden. Additionally, an adult son should refrain from looking at his mother.