Natural tones mean healthy scalps

 作者:鱼皈     |      日期:2019-03-08 08:01:01
By Andy Coghlan GO EASY on the hair dye if you want to keep your scalp healthy. So says a researcher who’s shown that commonly used dyes reduce the numbers of beneficial scalp bacteria. Stanley Lopez of the University of Memphis examined the effects of p-phenylenediamine, a popular brown dye. When he exposed bacteria to doses matching those recommended for dyeing hair, he found that they slowed down the growth of beneficial species including Staphylococcus epidermis and Micrococcus luteus. On a healthy scalp, these species exclude other bacteria that can cause infections and also fungi that cause dandruff. “If you reduce S. epidermis in particular, you leave the door open for these organisms,” says Lopez. The effect was even more pronounced when Lopez exposed the bacteria simultaneously to the brown dye plus a reddish dye called 2-nitro-p -phenylenediamine. People often apply the two together because the second dye intensifies the brown colour of the first. But Lopez found the second dye to be harmless when it was applied on its own to the bacteria. Staphylococcus aureus and Pseudomonas aeruginosa, two bacterial species that can cause infections,