There are several things that can lead to permanent loss of smell. When your smell is impacted, you also have limited taste sense. This is because it turns out we actually rely pretty heavily on smell and interpret this as taste. However, allergies and cold symptoms do not lead to permanent damage to the smell sense, so don't worry
. What has happen is simply that the nerves inside your nose that are responsible for smell have been covered over by the mucus and inflammation from the cold. Once the cold symptoms clear up, this should get a whole lot better!
If you are persistently having trouble with allergy symptoms such that they are affecting your quality of life, including your ability to smell or taste, then you should see your primary care doctor
about them. There are numerous medications and over the counter remedies that can be used to reduce the mucus congestion and nasal stuffiness that produce most of the symptoms associated with allergies. Often it is necessary to take a daily medicine to keep things under control, but these are usually well tolerated with minimal side effects. Your doctor will be able to help you decide what to do.