Infants with stiff necks may have high muscle tone, deformed strabismus, etc., and should seek prompt medical attention to find out the cause of the problem. 1. High muscle tone: It is due to the high muscle tone of infants, so it is easy to cause infants to have a hard neck when they tilt back. 2. Deformity of the inclined neck: ultrasound may indicate that the degree of thickening of the sternocleidomastoid muscle is not the same on both sides, and the affected side may be thickened, with fibrosis or ossification formation, which is tougher in texture, with poorer mobility and unclear boundaries, and the contracture deformity may pull the infant’s neck, resulting in the appearance of a stiff neck. There may be other reasons for the stiff neck of infants, it is recommended to go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.