Yes, if you allow moisture or even a small amount of water to mix with the oil, this can allow mold to grow over a very short period. The oil will no longer be usable if this happens. If you remove the lid be very careful not to allow water or moisture into the bottle.
We would recommend you do not remove the lid while you are in a room where there is additional steam or moisture present as this could allow moisture to enter the bottle. Normal use in a steam filled room should be fine but there is added risk when leaving the bottle in rooms susceptible to moisture.
Our products are 100% natural, which is a good thing, however they are sometimes susceptible to moisture due to being natural.