You pick a scent, a gorgeous one that smells like Vanilla caramel icecream and the bath bomb turns out perfect! You high five everyone and give yourself a pat on the back for a job well done. A week later however your beautiful white bomb turns into... a weird brown spotty.. creation? It has happened to most of us who are learning at some point. Most of those delicious bakery scents contain vanillin, which over time discolours in your products to brown.
So why would this happen?
Unfortunately, when vanillin is exposed to air (and light) the vanillin starts to go brown. It is a completely natural process and it can be fast or slow depending on what type of product it is in. This is because of the pH of the product and it gets browner the more alkaline it is. Bath bombs and soaps discolor quicker than the acidic products for example shampoos and lotions.
Solutions if you want to use fragrance oils with vanillin in your products!
1. The easiest one people gravitate towards is to use a vanilla stabilizer, an ingredient designed to prevent discoloring. Ensure you’re using the right stabilizer for the right product: There are different versions for lotions, melt & pour soaps, bath bombs, and so on. Be aware this does not fix the discolouration completely and forever, it simply slows down the discolouring. You will eventually still end up with brown but it might take weeks or months instead of a few days.
2. Package your products in a closed dark container to reduce exposure to light and air to slow down the process of oxidation. For most products, bottles with pumps or disc caps are a better choice than jars. When displaying keep them out of direct sunlight as much as possible.
3. You could add an anti-oxidant like Vitamin E at 0.05% to your product to slow down oxidation.
4. Add a whitener, like titanium dioxide. You only need a tiny amount and choose the right one for your product for oil or water-soluble before adding to the cool-down phase. Taking a small amount of the product out and mixing it well in a container before mixing it back into the whole batch will help you avoid clumps.
5. Add more colour! It might not work well with a lotion or other leave-on product, but a few extra drops of liquid colorant in a bubble bath or shower gel easily disguises the slight browning.
6. Plan for discolouration! It isn’t a bad thing for our product to brown. As you’ve seen, it doesn’t mean the product’s gone bad or is dangerous: It just isn’t as pretty as it could be without the slight discoloration. If you are making hot cocoa bath bombs then if it goes a darker brown that's totally fine! Another way would be if you mix the fragrance only into the dark parts of your bomb and leave the white parts unscented.
Did you know vanillin can also impact more than just the color of the product? Because it’s polar, it’s soluble in water. (Water is polar, oil is non-polar, and the rule is “like dissolves like”, so polar things usually mix well with water.) When including it in an anhydrous product, like lotion bars, whipped butters or paraffin candles, vanilla can show up as a light film on the surface or small droplets at the bottom of the container. If you’ve noticed this bloom and it bothers you, include a bit of a non-ionic solubilizer, like polysorbate 20 with the fragrance oil to make sure it stays emulsified.