A friend was just diagnosed with environmental allergies, is that a serious condition?

Depends on meaning: And meaning depends on who made the diagnosis. As an allergist when i say that someone has environmental allergies i mean that things like house dust mite, plant pollens, animal dander & mold spores are triggering symptoms of allergic rhinitis, allergic conjunctivitis, asthma & sometimes eczema & hives. These are common medical conditions that while sometimes serious are rarely life-threatening.

It can be: Allergies to environmental allergens such as pollens, molds, danders and dust mites can be easily controlled in most patients. If left untreated, however, in addition to making people miserable, chronic allergic inflammation can lead to chronic sinusitis, ear problems, and asthma. For the most part these are not life-threatening, but they can significantly interfere with the quality of life.