Winter is associated with some of the triggers for cold sores:^1-7 

• Cold weather 
• Fever due to illnesses such as a cold or flu 
• Reduced immunity increases susceptibility to viral infections 
• Chapped lips caused by cold weather, chilling winds or excessive licking 
• Fatigue 

FAST FACTS 

• Cold sores are caused by the herpes simplex virus (HSV)⁸ 
• HSV-1 is primarily responsible for oral cold sores, and HSV-2 is primarily associated with genital herpes but HSV-2 can also cause lesions on the lips^8-10 
• The virus can spread from person to person, even if there are no visible symptoms⁸ 
• After the primary infection in the skin the HSV-1 spreads to the peripheral nervous system, where it lies dormant in the trigeminal ganglia (facial nerve)^8,10 
• The virus can reactivate when triggered and travel back along the axon to replicate in the local surrounding tissue to cause a latent infection.^8,10 Common triggers include: emotional stress, sunlight, menstruation, fever and physical trauma⁸ 

REFERENCES 

1. Gopinath, D., et al. Comprehensive Overview of Epidemiology, Pathogenesis and the Management of Herpes Labialis. Viruses 15, 225 (2023). https://doi.org/10.3390/v15010225.  
2. Huang D., et al. Cold exposure impairs extracellular vesicle swarm-mediated nasal antiviral immunity. Mechanisms of allergy/immunology. 151(2), P509-525 (2023).  
3. What Causes Chapped Lips and How to Treat Them. [Internet] Healthline 2023 (cited: November 
4. 2023) Available from: https://www.healthline.com/health/chapped-lips#treatment (2023).  
5. Cold weather: protect your mouth. [Internet] UK HealthCare (cited: November 2023) Available from: https://ukhealthcare.uky.edu/sites/default/files/cold-weather-protect-your-mouth.pdf.  
6. Can cold sores be prevented? [Internet] Institute for Quality and Efficiency in Health Care (IQWiG); 2018 (cited: November 2023) Available from: https://www.ncbi.nlm.nih.gov/books/NBK525765/  
7. Fonte A., et al. Seasonal sensitivity and psychiatric morbidity: study about seasonal affective disorder. BMC Psychiatry 21,317 (2021). https://doi.org/10.1186/s12888-021-03313-z. 
8. Pringle, C. R. Merck Manual. Merk Manual (Merck Sharp & Dohme Corp., 2018).  
9. Grinde B. Herpesviruses: latency and reactivation – viral strategies and host response, J Oral Microbiol 2013;5:22766. DOI: 10.3402/jom.v5i0.22766.  
10. Bello-Morales, R.; Andreu, S.; López-Guerrero, J.A. The Role of Herpes Simplex Virus Type 1 Infection in Demyelination of the Central Nervous System. Int. J. Mol. Sci. 21, 5026. https://doi.org/10.3390/ijms21145026 (2020).