Skin Allergies. Your Great Dane can have an allergy to something as simple as grass or the laundry detergent you've been washing his favorite blanket with! Allergic Dermatitis is usually characterized by redness, swelling, itching, flaking, and runny eyes. It can be caused by anything, including hormonal imbalance. Sometimes the culprit is parasites (think along the lines of fleas and mites). Your veterinarian can offer alternatives to sooth your Great Dane from discomfort.