It is possible to be allergic to the liquid form of amber?
It is possible to be allergic to almost any substance. Only a doctor can tell you for sure, through proper testing.
An allergic reaction to a banana isn't very common, but it does happen. Some people are allergic to the form of protein contained in the banana. Additionally, if you're allergic to the banana, you could also be allergic to watermelon, cantaloupe kiwi, avocado and chestnuts and latex. Some people aren't actually allergic to bananas, they're allergic to the gas used to ripen bananas.
Nitrogen mustard is used in chemotherapy. It also has the potential to be a weapon of terror so its manufacture and use is closely monitored. Nitrogen mustards can be clear, pale amber, or yellow colored when in liquid or solid form. The yellow mustard color accounting for its designation as "mustard." It is not the mustard gas that was used in WWI. It is a man made substance and liquid at room temperature.