Back in the day, I used to spend so much on fancy candles from Yankee Candle...from Balsam Pine to Sage & Citrus, they had me at hello. Little did I know that these scents contained endocrine disrupting fragrances and petroleum based wax.
Many candle makers use paraffin wax which is derived from petroleum. The problem with that is when burned, paraffin wax releases particulate pollution which can irritate the eyes, skin, and respiratory system. It can also cause adverse health reactions, such as difficulty breathing, headaches, nausea, and heartburn. Paraffin wax contains chemicals like benzene, toluene, and naphthalene, which are associated with asthma, respiratory conditions, and allergy-like reactions.
Coconut soy wax doesn't release harmful chemicals and burns cleanly with little soot. I love using coconut soy wax because it burns so clean and doesn't irritate my allergies.
Beeswax candles are another amazing option for purifying the air but adding scent to them is tricky because most essential oils are degraded by heat so it's better to just use unscented beeswax.
Now what about fragrance?
Back in 2012, I started making soap and quickly discovered things like phthalates and parabens which are in fragrance oils and other bath & beauty product ingredients. I searched for an alternative to fragrance oils and began using essential oils in soap, but some of them just didn't stick and left the final product pretty bland (and wasted super expensive oils). I wanted to make sure that any fragrance oil I used was paraben & phthalate free, but still had concerns about other constituents that could potentially be harmful.
Like I said earlier, essential oils are tricky in candles because the fragrance throw can actually be degraded by heat so a lot of essential oils don't "stick" like as in soap - this basically means they evaporate much quicker and much more easily than fragrances oils. (Long story short-a lot of wasted money on essential oils in candles) A lot of them can be broken down by heat and can become toxic when burned. 
So that leaves fragrance oils, but they're all bad, right? Well, turns out not all are created equally...
CandleScience has a line of certified clean scents that meet my specifications for using in my home. They are phthalate free and don't contain any ingredients on California's Prop 65 list. Here's a list from their website of hazardous ingredients they avoid.
Additionally, these Clean Scents™ avoid 5 main hazard groups:
✖ Carcinogens: These are materials known or thought to cause cancer.
✖ Mutagens: Materials that change the DNA of a cell, harming the cell and causing diseases like cancer.
✖ Reproductive toxins: Toxins that adversely affect reproductive organs and increase the risk of birth defects.
✖ Organ toxins: These are toxins that can cause adverse effects or disease within specific bodily organs.
✖ Acute toxins: Toxins that can cause adverse effects from a single exposure. Generally, this would be accidental exposure like spillage or ingestion.
So while there are a lot of fragrance oils on the market today, you can rest assured that the ones in our products are non-toxic.