Hoarseness in three-month-old infants may be caused by excessive crying, developmental abnormalities, respiratory tract infections and other reasons. 1. Excessive crying: three-month-old babies often have colic, bloating and other gastrointestinal symptoms, which may cause babies to cry constantly, when crying for a long time may lead to damage to the vocal cords, hoarseness of the voice. 2. Developmental abnormalities: when three-month-old infants have congenital pharyngeal developmental abnormalities and other diseases, such as vocal polyps, vocal edema, pharyngeal cysts, etc., may affect the function of the vocal cords, resulting in hoarseness. 3. Respiratory infections: hoarseness in three-month-old infants may also be caused by respiratory infections, pharyngitis and other causes, in addition to coughing, nasal congestion, runny nose and other conditions. Three-month infant hoarseness, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.