Locating semen stains on clothing usually relies initially on a chemical screening test followed by a microscopic examination for spermatozoa (sperm cells) to confirm the presence of semen. But are the tests used sensitive enough to detect semen after an item has been washed?
The term ‘washed’ can mean many different things ranging from a quick rinse, a full wash cycle in a washing machine or soaking and then washing for example. How long the item is immersed in water, the type of detergent and temperature used will have some effect on whether semen can be detected afterwards. A scientist will need to be given as much information as possible about the type of washing used so that they can advise on the likelihood of detecting any staining and decide what tests and strategy they should employ. This is also relevant when an expert is asked to comment on whether stains are likely to be found on a washed item, and whether the laboratory testing was appropriate.