1. Lice infestation: itching and skin irritation caused by lice can lead the Shih Tzu to scratch, rub, and chew itself. The coat in affected areas becomes rough, dull, easy to break, and easy to shed. Heavy lice infestation can cause significant hair loss, and large amounts of shed hair may be found in places where the dog often stays.
2. Vitamin deficiency: a lack of vitamin B in a Shih Tzu can also cause hair loss. At the same time, the dog may show signs such as weight loss, poor appetite, general weakness, and decreased or even lost vision.
3. Estrogen imbalance: this is more common in adult unspayed female dogs. It is characterized by excessive estrogen secretion, generalized itching, hair loss that is often symmetrical, and increased skin pigmentation. Some affected dogs also have a swollen vulva, bloody discharge, and signs resembling a prolonged heat cycle.
4. Mange: this may be caused by sarcoptic mites or Demodex mites. Sarcoptic mange usually appears on the head, especially the bridge of the nose, around the eyes, the ear flaps, and the base of the ears, but it may also affect the chest, underside of the abdomen, armpits, inner thighs, and the side of the tail, and may even spread throughout the body. The skin becomes reddish and develops small rash-like nodules, while the tissue underneath thickens. Frequent scratching, rubbing, and chewing then cause hair loss. Demodex mites mainly cause localized patches of hair loss around the eyes, though in some cases the condition can spread across the whole body. The affected skin becomes thickened and scaly, and sometimes it can develop into pustules or purulent dermatitis.