Have you read this article from WYZA? It's called 23 Subtle Ways Your House Might Be Making You Sick.
In it, Alyssa Jung and Tina Donvito share their insights. Here's one that's really interesting:
If you’re obsessed with keeping your house smelling fresh, you could be affecting your health. Scented candles, oil diffusers, plugin fresheners, and scented sprays may contain phthalates, chemicals that may disrupt the endocrine system by interfering with hormones.
If you wish to know more, give the rest of the article a read.