Trace evidence occurs when objects make contact, and material is transferred. This type of evidence may not even be visible to the naked eye and requires specific tools and techniques to be located and obtained. Microscopic hair and dead skin cells can be collected, as well as droplets of blood, saliva, or semen for DNA evidence. Fingerprints can be identified but may also leave secretions, skin oils and dead cells which show chemicals and metabolites present in the body at the time. Forensic identification is the application of forensic science and technology to identify specific objects from the trace evidence they leave.