Oxytocin (sold as Pitocin, Syntocinon) is a mammalian hormone that acts primarily as a neurotransmitter in the brain. Russell Wright and Sue Bell of Theme Zoom often speak about this neurochemical as the "touch-me-feel-me" drug secreted by the brain. It is also intrinsically related to social bonding and trust building, and is triggered in response to (but not limited to) visual stimulus such as seeing a familiar or pleasant face.
This is obviously important knowledge in the field of Neuromarketing. Even though the clinical study of oxytocin is a complex and controversial subject it can be considered the "trust bond" chemical. Oxytocin drives a mother to nurture and cuddle her young. It also drives a female (and to a lesser extent a male) to crave soft touch and caressing. Males have less oxytocin unless it is cultivated.
Oxytocin is different than dopamine in that it is about trust and trust building. When you see the face of a familiar friend or family member (for example your mother) your oxytocin levels will increase.
If someone violates your trust, your oxytocin will decrease when you see their face.
Listen to Russell Wright provide a brief audio overview on the brain chemical oxytocin. (recommended)