A strong mustard can cause the eyes to water, sting the palate, and inflame the nasal passages and throat.

Mustard can last indefinitely, though it may dry out, lose flavor, or brown from oxidation. Mixing in a small amount of wine or vinegar will often revitalize dried out mustard. Some types of prepared mustard stored for a long time may separate, which can be corrected by stirring or shaking. If stored for a long time, unrefrigerated mustard can acquire a bitter taste.