Why does my dandruff shampoo make my hair smell like rotten eggs?

Cathy inquires…I occasionally suffer from itchy scalp but this morning I was out of my usual Fructis dandruff shampoo so I used my roommates Head and Shoulders. The one in the dark blue bottle. I swear that my hair has smelled like rotten eggs all day. Why is that and why did this product cause it when others don’t? I thought all dandruff shampoos were essentially the same except for color and fragrance.

The Beauty Brains respond:

The majority of dandruff shampoos use zinc pyrithione (ZPT) as the active ingredient. For most people that’s sufficient to alleviate their symptoms. But the Over the Counter Drug monograph that controls the active agents that can be used in these shampoos includes other options for those people who don’t respond well to ZPT.

One of those options is selenium sulfide which works by reducing corneocyte production and an antifungal mechanism that is yet unknown. As many sulfur containing compounds do , selenium sulfide can have a residual sulfur odor that is very reminiscent of rotten eggs. The Clinical Strength variety of Head and Shoulders (the one in the dark blue bottle) uses this eggy ingredient. If your typical Fructis shampoo works for you stick with it and let your room mate be the egg head.