Infants and toddlers cry as a manifestation of physiological needs and discomfort from illness. The causes of crying are complex, divided into physiologic and pathologic crying, and are a frequent challenge for pediatricians. In particular, excessive crying is considered to be one of the most common symptoms encountered by pediatricians, with an estimated prevalence of 4% to 50%, of which only a small percentage (perhaps 5% to 10%) is due to organic and/or caregiver psychological abnormalities. To determine if the crying is physiological, first note the size, quality and tone of the child’s cry. Normal infants cry loudly, quietly and in tune. Weak cries can be seen in a state of failure due to various pathological reasons, such as hypothyroidism, vocal cord paralysis, laryngitis or congenital laryngeal cartilage dysplasia; high pointed cries are mostly seen in intracranial hemorrhage, hydrocephalus, etc. Special cries suggest some special diseases such as catcall syndrome. Next, we should pay attention to the causes of crying, such as the presence of hunger, whether to urinate or defecate, whether there is fatigue and sleepiness, whether there is local stimulation such as clothing discomfort, and whether there is a change in the routine of life. Finally, pay attention to the symptoms accompanying crying, such as fever, cough, vomiting, and convulsions. Diagnostic steps Step 1: Determine whether the crying is physiological or pathological Physiological crying is generally good, and the child cries loudly and in tune. In pathological crying, the child has other symptoms or signs, such as fever, multiple deformities, etc. The second step: physiological crying should be identified as the cause, and the crying will stop after the cause is removed. Hunger is the most common cause of physiological crying in newborns and small infants, and the crying will stop immediately after feeding or water. Newborns can cry before urination or defecation due to bladder or rectal filling discomfort. More common reason is that after urination or defecation, wet diapers or clothing, local skin irritation causes crying, and crying stops after changing clean clothing. Many children cry when they are tired and sleepy, and the crying stops when they are soothed to sleep. Teeth eruption can be painful when passing through the periosteum, and teething is a common cause of crying in some patients. Some infants have reversed day and night sleep cycles and cry at night, but most of these children have increased daytime sleep, and they have a good mental appetite and good body mass growth. It is important to diagnose crying due to disturbances in the child’s routine with caution, to exclude pathological crying and to understand the manifestations of excessive crying in children. Only 5% of excessive crying is caused by organic diseases. The three characteristics of crying in infants and young children are as follows: Age-dependent: The first thing to define is that crying has age-dependent and daily characteristics. The age-dependent characteristic refers to the typical increase in colic-like crying that begins about 2 weeks after birth, usually peaks in the second month, and decreases to its initial level about the fourth month of life. The daily characteristic is that the crying is more likely to occur in bouts later in the afternoon and at dusk. In fact, these are 2 aspects of the same phenomenon, because the age-related increase or decrease in crying is mainly related to the change in the amount of crying that is manifested by the occurrence of bouts of crying later in the afternoon. Associated behavioral features: The second definition is that crying tends to have many accompanying behavioral features, 2 of which are almost always present, while others are optional. 2 common features are prolonged bouts of crying (sometimes called “colic” episodes) in which all kinds of soothing do not work, even feeding. During these episodes, the infant may also clench his or her fists, bend his or her legs to the abdomen, arch his or her back, have a vivid and varied facial expression, giving the impression that the infant is in great pain (“pain face”), and have a flushed face. This is generally considered a gastrointestinal problem, and the infant may have abdominal distention and abdominal muscle tension, and crying episodes may be accompanied by gastroesophageal reflux and anal discharge. Episodic: The third definition is typical of crying episodes as paroxysms, which occur suddenly and abruptly without any warning and are not easily influenced by other factors in the environment (spontaneous appearance). Step 3: Define the cause of pathological crying First take the temperature. If fever is present, consider infectious diseases. If the child has an infectious disease, he or she will have non-specific manifestations such as irritability and crying, and the corresponding diagnosis will be made based on other symptoms such as cough, diarrhea and vomiting. Next, we should pay attention to the child’s history of trauma, vitamin D deficiency, vitamin D overdose and exposure to other drugs or toxins. The physical examination should pay attention to the presence of localized redness, swelling and bleeding in the bones and joints, and the presence of focal lesions such as skin eruptions, eczema, heat rash, oral ulcers, thrush, etc. The presence of signs of increased intracranial pressure, such as bulging fontanelle, optic nerve disc edema, etc. Signs of rickets, such as occipital baldness, square cranium, softening of the skull, rib cage beads, etc. The presence of abnormalities in appearance and other multiple deformities. Abdominal pain is a common cause of crying in children Sharp cries suggest severe pain. There are many causes of abdominal pain, which can be caused by gastrointestinal spasm or by some organic lesions such as appendicitis and intestinal obstruction. Vitamin D deficiency rickets This disease mostly occurs in children aged 3 months to 2 years. The main causes are insufficient sunlight, insufficient intake of vitamin D-containing foods, and some disease factors such as gastrointestinal diseases that affect the absorption of vitamin D or liver and kidney diseases that affect the hydroxylation of vitamin D. At the beginning of vitamin D deficiency rickets, children are more restless, crying and startled, and then typical skeletal changes appear, such as cranial softening, square skull, bracelet sign, ankle bracelet sign, delayed closure of fontanelle and cranial suture, and delayed teething. Carpal bone X-ray showed cup-shaped changes in the distal ulnar and radial bones, blurred temporary calcified bands, and decreased bone density. Blood calcium and phosphorus are reduced or normal, and alkaline phosphatase is elevated. Vitamin D toxicity Mostly caused by parents giving children improper vitamin D and excessive intake. If the intake is 20,000 to 50,000 U/d or 2000 U/kg, poisoning can occur after several weeks or months of continuous use. It can also occur in sensitive children with 4000 U/d for 1 to 3 months. At the beginning of vitamin D toxicity, symptoms similar to the early stage of vitamin D deficiency rickets such as irritability, crying and excessive sweating may appear, and in severe cases, convulsions, increased blood pressure, cardiac arrhythmia, thirst, frequent urination, dehydration, acidosis, proteinuria, hematuria and chronic renal failure may occur. Blood calcium >3 mmol/L, X-ray shows abnormal calcification of bones, and in severe cases, there are foci of calcification in the brain, blood vessels, heart, kidneys and skin. Vitamin A toxicity A history of excessive vitamin A intake, clinical symptoms of acute or chronic intracranial pressure elevation, irritability, crying, vomiting, and bulging fontanelle in children. Chronic toxicity may also present with rough, flaky skin, chapped corners of the mouth, and thinning hair. Serum vitamin A concentration is >5.1 mmol/L. Hyperthyroidism in newborns whose mothers have hyperthyroidism may cause excitement, hyperactivity, crying, restlessness, panic attacks, lack of body mass, often cardiac insufficiency, hepatomegaly, and jaundice. Laboratory tests show elevated T3 and T4 and decreased TSH. Catcall syndrome is called catcall syndrome because the child cries faintly like a cat. It is usually seen in children with low birth weight, small head circumference, wide eye spacing, oblique outward eye fissures, broad and flat nasal bridge, small jaw, high palatal arch, often accompanied by inguinal hernia, multiple malformations of the heart, kidneys and bones, low intelligence, and chromosomal examination can confirm the diagnosis. Symptomatic and etiological treatment First of all, a detailed medical history should be taken and a careful physical examination should be performed to remove the causes of physiological crying such as hunger, discomfort in clothing, urination and defecation. If the cause is clear, etiological treatment should be given quickly. In case of acute abdominal disease such as gastrointestinal perforation or obstruction, surgery should be performed as soon as possible. In case of infectious diseases, effective antibiotics or antiviral drugs should be given as soon as possible.