Symptoms of strep throat usually begin within 2 to 5 days after you come in contact with someone who has a strep infection. Strep throat usually goes away in 3 to 7 days with or without antibiotic treatment. In contrast, if allergies or irritants are the cause of your sore throat, it will usually last longer unless the cause is eliminated.
If strep throat isn't treated with antibiotics, you will continue to be contagious for 2 to 3 weeks even if your symptoms go away. You are much less contagious within 24 hours after you start antibiotics and are less likely to develop complications of the strep infection.
Complications of strep throat
Complications of strep throat are rare but can occur, especially if your throat infection isn't properly treated with antibiotics. Complications can occur when the strep infection spreads to other parts of the body and causes other infections, such as an ear or sinus infection or an abscess near the tonsils (peritonsillar abscess). Complications can also result in your immune system attacking itself and causing serious conditions such as rheumatic fever.
Treating strep throat can greatly reduce your risk for rheumatic fever and its complications. It is not clear whether treating the strep infection with antibiotics reduces your risk for inflammation of the kidneys (acute glomerulonephritis).