Why It Happens: Many allergies, like hayfever, can cause the nose to run copiously. The resultant irritation to the nasal membranes, and the frequent nose blowing resulting from this, can lead to nosebleeds.
Additional Info: Many medications for allergies, in particular nasal decongestants, can cause drying of the lining of the nose, further increasing the incidence of nosebleeds.
What To Do: If you do suffer from allergies, consider using supplements to boost your immune system to help reduce the incidence and severity of the allergic reaction. Vitamin C and carotenoids will both assist. Make sure you get supplements that are organically derived from whole-food based sources for best results.