Essential Oil shelf life?

[Guest guest]

I'm working on starting an aromatherapy line to complement my work as

an LMBT, and I've noticed that all my bath salts tend to lose the

fragrance of whatever essential oils I've used in them after about a

week. I'm still working on getting the portions and recipes right so

I'm just keeping them stored in ziploc bags in cool, dark places. Are

the bags making the EO's 'expire', is there a fixative I should be

adding, or do I just have a bad batch of EO's? Typically I use one

portion of epsom salts, one portion of coarse sea salts, sometimes a

little vitamin E, and usually a total of 10 drops of various EO's.

This problem isn't present in any other medium (carrier oils, etc.),

just the bath salts.

 

What am I doing wrong?