Incense and scented candles are headache fodder for me..

Plus any kind of plug-in or spray air freshener...

Re incense, it's down to possible benzine and formaldehyde. Very zen (not) and the cheaper the sticks the more likely they will contain these chemicals - hence the headaches.

We don't use them in our house now because I kept getting headaches and while my triggers are numerous I realised that I was getting headaches whenever I used them. Also whenever I went into a shop which had some burning..

Hubs used a cone one a few months ago because I was upstairs but the smoke came up through the floorboards and I still got the headache so they're completely banned now. We only use essential oil in diffusers and I only use the pure stuff. I never use those cheap perfume thingies..

Essential oils (the pure ones) are beneficial health wise but I'd advise buying the best that you can afford from reputable companies.

A tip to make the house smell nice is to throw a few cinnamon sticks into a saucepan of hot water. I also put little cotton wool balls behind my radiators with a few drops of essential oil on them so the house smells nice when the timer kicks in..

I do this to freshen up my stinky hoover...

I also make my own version of 'Shake 'n' Vac' by using a few drops of essential oil into some bicarbonate of soda. It freshens up the carpet and with no nasty chemicals..