When I began using essential oils in my everyday life not too long ago, I didn’t pay much attention to the hows and whys of proper oil storage. I was more focused on what I could do and make with the oils. I just kept in mind that these needed to be contained properly and followed Young Living’s guide, putting the oils I mixed in the small amber bottles that came with my essential oils starter kit.

Then one day, I was mixing lavender, peppermint, and thieves with Purification to use on my air diffuser for the office. As I put them back in the kit one by one, I paused for a moment and studied the bottle in my hand. I began to wonder.

Why is it essential–pun intended–to store them properly?

After some further reading, I learned a very important thing about these essential oils that I’ve grown very fond of:

The oils are very sensitive to heat and sunlight. Although they don’t turn stale, they will, however, lose their therapeutic properties over the course of time if not stored properly.

Now, why amber bottles?

The answer is actually very simple. Amber’s dark color helps protect essential oils from the light and the heat. Though the highest graded oils like Young Living have no expiration dates, their quality will still deteriorate if you don’t take care of them.

Essential oils aren’t the only ones that benefit from amber—there’s a reason why a lot of pharmacy bottles are also in that color. Medicine can also be affected by light and temperature.

If you’re thinking of using plastic bottles, don’t. Essential oils can eat through plastics and absorb some of their chemicals, affecting the oils’ therapeutic benefits. Glass bottles in other colors like dark blue or green are becoming popular these days, but they can allow the other colors of light into the container and damage the essential oils. It’s best to stay with old reliable amber.

The best essential oils are, admittedly, not cheap, but they’re definitely a worthy investment when you take good care of them. If you want to make every drop in that bottle count, you better start storing them the right way.