Synthetic musks are a group of chemicals that are manufactured to emulate natural musks. They are found in substances such as aftershave, soap, perfume and air fresheners.
These musks are absorbed through the skin and lungs and some, due to their structure are thought to be endocrine disruptors. They are stable substances so they tend to persist in the environment (hence the reason why they are used).
This is a molecule of Galaxolide, a synthetic musk.
This image was kindly reproduced according to the licence at: http://en.wikipedia.org/wiki/File:Galaxolide.svg