I applied BT to my scalp on Thurs night and the following morning I went to the gym. Everything was OK until I went into the sauna to (pre-poo with heat/condish) and after about 10 mins, I distinctly caught the whiff of sulphur wafting through the hot air! I personally thought it was quite strong. I should add, however, that I'd been using it every other day since my last wash on the previous Monday, so there was already a build up and not just the one application. Good thing I was the only one in the sauna at the time. Other than that, it doesn't run down my scalp or anyting with a previous night's application, nor does it smell at all otherwise. I have the scented one.