1. American Lung Association https://www.lung.org/lung-health-and-diseases/lung-disease-lookup/influenza/facts-about-the-common-cold.html
2. Centers for Disease Control and Prevention, USA https://www.cdc.gov/antibiotic-use/community/for-patients/common-illnesses/colds.html
3. Mayo Clinic, USA https://www.mayoclinic.org/diseases-conditions/common-cold/symptoms-causes/syc-20351605
4. MedicineNet https://www.medicinenet.com/common_cold/article.htm
5. MedlinePlus, U.S. National Library of Medicine https://medlineplus.gov/commoncold.html