Hair color remover is the assistant of murderers

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Chemicals that people often use to bleach hair may disable the medical doctor's blood detection techniques when investigating homicide.

There are two common types of hair bleaches. Bleach containing chlorine causes blood stains to become 'invisible'. But if you use chemicals like luminol and phenolphthalein, forensic staff can still detect hemoglobin (the oxygen-carrying protein of red blood cells). However, with a second detergent containing oxygen, all traces of hemoglobin will be wiped clean.

To test, scientists at the University of Valencia (Spain) dipped cloth with blood stains on oxygen-containing detergent for 2 hours and compared the results with untreated blood samples. They found blood stains fading after the cloth was dipped in detergent but still visible. However, they could not detect traces of hemoglobin in the fabric after using luminol, phenolphthalein and other direct inspection measures.

Meanwhile, chlorine cleaners can produce false positive results if forensic staff uses luminol to look for traces of blood. However, experts have many ways to deal with this phenomenon. For example, one can conduct further tests to determine if the positive result is correct. But oxygen-containing detergents pose a much bigger challenge.

'Forensic experts will only search for DNA when they find human body tissue. If measures for the presence of hemoglobin are negative, they will conclude that there is no blood. So they will miss the opportunity to get more information about the case, 'said Jonathan Creamer, an expert at Vanderbilt University (Tennessee, USA).