Baby always crying in the middle of the night, may be caused by physiological factors, may also be due to vitamin D deficiency, eczema and other pathological factors. 1. Physiological factors: babies eat too much or hungry before going to bed, the environment temperature is too high or too low, may lead to the baby always crying in the middle of the night, just need to remove the triggers can be. 2. Vitamin D deficiency: it often leads to crying, night terrors, occipital baldness and excessive sweating. Later on, it can also appear X-shaped legs, O-shaped legs and other bone deformation. 3. Eczema: a highly prevalent disease in infants, usually leading to itching, pain, etc., manifested in the appearance of skin patches, maculopapular rash, papules, scaly hyperplasia, skin thickening. The baby always cries in the middle of the night, there may be other problems such as otitis media, it is recommended to consult a doctor in time to find the cause and scientific treatment.