Hello, Sinusitis in children can be caused from viruses, allergies, or bacteria. Acute viral sinusitis is likely if your child has been sick for less than 10 days and is nor getting worse. Acute bacterial sinusitis is likely when the sinusitis symptoms do not improve at all within 10 days of getting sick, or if your child gets worse within 10 days after beginning to get better. Chronic sinusitis last 12 weeks or longer, and is usually caused by prolonged inflammation, instead of a lung infection. Recurrent sinusitis when the infection comes back again and again. It means 3 or more episodes of acute sinusitis in a year. A sinus infection sometimes happens after an upper respiratory infection or common cold or allergies. They cause welling nasal cavity meat (turbinates) that can block the opening of the sinuses. This can cause sinus infection and increase mucus. but also have the other causes like the abnormal shape of the nose, infection from the tooth, nose injury, foreign object in the nose, stomach acid. To be sure what is the real diagnosis in a child at my practice I would like to know clear history and examination and do image study. Treatment will depend on your child s symptoms, age, and general health. It will also depend on how severe the condition is. Antibiotic help your improve after 3 to 5 days if the sinuses infection from the bacteria. and if not improve 3 to 5 day your doctor may try a different antibiotic. Allergy medicines (antihistamines) for siniusitis cause by allergy. For chronic sinusitis your child better get corticosteroid nasal sprays (Desolex) or drop and antihistamine to decrease swelling and mucus to open your child upper airway and mucus flow easily. Like that it can prevention sinus infection again. For Prohist syrup, it is combination medicine contain of decongestants and antihistamine. Decongestant medicine we do not recommend long term treatment because it may cause serious side effect such as rebound congestion, decrease blood flow to the kidney, hypertension, slow heart rate. Mostly we use just a short term period. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Heang Chan Raksmey, General & Family Physician