During the summer, certain conditions increase in prevalence due to seasonal factors, such as changes in heat, humidity, and human activity. The most common summer illnesses fall in two categories: environmental conditions, ranging from heat exhaustion to sunburn to allergies and respiratory conditions; and infectious diseases, ranging from foodborne illnesses to vector-borne diseases. From heat-related conditions to insect-borne diseases, understanding the heightened prevalence of common illnesses during the summer can help everyone take steps to reduce the risks.

First, with the increased temperatures, sun exposure, and physical activity, rates of mild and severe conditions related to environmental exposure rise significantly during the summer months. Sunburn, the most common condition, affects millions of individuals every year, with 20 to 34% of adults and 69% of adolescents experiencing at least one sunburn every summer (1). Although overexposure to the ultraviolet rays in sunlight can lead to skin cancer, the majority of sunburns are benign, and the damaged skin typically heals within 3 to 5 days (2). Dehydration, another typically mild condition, commonly affects individuals, causing symptoms of fatigue, headache, dizziness, muscle cramps, and flushed skin (3). Mild to moderate cases can be alleviated with an electrolyte-rich beverage, but severe cases require hospitalization (3).

Severe heat-related illnesses that are common in hot summer months include heat exhaustion and heat stroke. Although these two conditions are often conflated, each term represents a specific stage in the physiological response to overheating (4). Heat exhaustion appears first, presenting with dizziness, excessive sweating, nausea or vomiting, muscle cramps, a weak pulse, and cool, pale, clammy skin (4). This condition can be ameliorated by drinking water, moving to cooler temperatures, and loosening clothing (5). If symptoms do not improve, the condition can progress to heat stroke, an advanced stage of overheating. In contrast to heat exhaustion, heat stroke involves a lack of sweating, severe headache, strong pulse, confusion or loss of consciousness, a body temperature higher than 103 degrees Fahrenheit, and hot, dry skin (4). Heat stroke requires immediate hospitalization, as the condition can result in organ damage; it results in the deaths of up to 58% of admitted patients within 28 days of onset (6). In recent years, as global temperatures rise, heat-related deaths have significantly increased, especially in older adults (7).

Other conditions linked to environmental exposure during the summer include asthma and other respiratory conditions. In asthmatic individuals, breathing in warm, humid air can narrow the airways, resulting in asthma attacks (8). Additionally, summer allergens — such as mold, ragweed and pollen — can exacerbate symptoms in individuals with allergies or allergic asthma (9). Thus, the combination of the climate, seasonal allergens, and increased outdoor activity can lead to exacerbation of respiratory symptoms in individuals with asthma or allergies.

Second, the heat of the summer months causes a rise in bacterial and vector-borne illnesses. While most pathogens survive year-round, summer heat and humidity provide an ideal climate for bacteria, mosquitoes, ticks, and other vectors to multiply rapidly (10). For example, E. coli and salmonella infection, two of the most common forms of bacterial disease, peak during the summertime (10, 11). Other vector-borne illnesses that are more common in summer include Lyme disease, transmitted by ticks, and West Nile virus, transmitted by mosquitoes (12). Symptoms from vector-borne diseases can appear mild, as in most cases of bacterial food poisoning, or severe, as in rare cases of West Nile virus.

In summary, the increased heat, humidity, and outdoor activity during the summer intensify the risks of developing environmental conditions, such as heat-related conditions and allergies, and vector-borne illnesses, such as salmonella and Lyme’s disease. To avoid heat-related conditions, experts at the Centers for Disease Control and Prevention suggest maintaining adequate hydration, applying sunscreen, and decreasing activity during the hottest hours of the day (13). Similarly, wearing long-sleeved clothing, using insect repellant, and practicing food hygiene techniques are recommended to avoid vector-borne diseases (14). Although the warm weather and outdoor activities may be the most exciting parts of the summer, it is crucial to practice these measures to avoid illness.

References

1: Buller, D., Cokkinides, V., Hall, H., Hartman, A., Saraiya, M., Miller, E., Paddock, L., and Glanz, K. 2011. Prevalence of sunburn, sun protection, and indoor tanning behaviors among Americans: review from national surveys and case studies of 3 states. Journal of the American Academy of Dermatology, vol. 65. DOI: 10.1016/j.jaad.2011.05.033.

2: Sissons, C. 2015. How long does a sunburn take to heal? Medical News Today. URL: https://www.medicalnewstoday.com/articles/319793#what-is-sunburn.

3: Costa, P. 2017. What you should know about dehydration. Medical News Today. URL: https://www.medicalnewstoday.com/articles/153363.

4: Gauer, R. and Meyers, B. 2019. Heat-related illnesses. American Family Physician, vol. 99. URL: https://www.aafp.org/pubs/afp/issues/2019/0415/p482.html.

5: Glazer, J. 2005. Management of heatstroke and heat exhaustion. American Family Physician, vol. 71. URL: https://www.aafp.org/pubs/afp/issues/2005/0601/p2133.html.

6: Hifumi, T., Kondo, T., Shimizu, K., and Miyake, Y. 2018. Heat stroke. Journal of Intensive Care, vol. 6. DOI: 10.1186/s40560-018-0298-4.

7: Vicedo-Cabrera, A., Scovronick, N., Sera, F., Roye, D., Schneider, R., Tobias, A., Astrom, C., Guo, Y., Honda, Y., Hondula, D., Abrutzky, R., Tong, S., Zanotti, M., Saldiva, P., Lavigne, E., Correa, M., Ortega, N., Kan, H., Osorio, S., Kysely, J., Urban, A., Orru, H., Indermmitte E., et al. 2021. The burden of heat-related mortality attributable to recent human-induced climate change. Nature Climate Change, vol. 11. DOI: 10.1038/s41558-021-01058-x.

8: Rossiaky, D. 2022. Asthma: why it can be worse during the summer. Healthline. URL: https://www.healthline.com/health-news/why-asthma-can-be-worse-during-the-summer.

9: Schmidt C. 2016. Pollen overload: seasonal allergies in a changing climate. Environmental Health Perspectives, vol. 124. DOI: 10.1289/ehp.124-A70.

10: Freeman, T., Anderson, D., and Sexton, D. 2009. Seasonal peaks in Escherichia coli infections: possible explanations and implications. Clinical Microbiology and Infection, vol. 15. DOI: 10.1111/j.1469-0691.2009.02866.x.

11: Akil, L, Ahmad, A., and Reddy, R. 2014. Effects of climate change on salmonella infections. Foodborne Pathogens and Diseases, vol. 11. DOI: 10.1089/fpd.2014.1802.

12: Caminade, C., McIntyre, M., and Jones, A. 2019. Impact of recent and future climate change on vector‐borne diseases. Annals of the New York Academy of Sciences, vol. 1436. DOI: 10.1111/nyas.13950.

13: Centers for Disease Control and Prevention. 2022. Tips for preventing heat-related illness. CDC Natural Disasters and Severe Weather. URL: https://www.cdc.gov/disasters/extremeheat/heattips.html.

14: Centers for Disease Control and Prevention. 2022. Prevent tick and mosquito bites. CDC Division of Vector-Borne Diseases. URL: https://www.cdc.gov/ncezid/dvbd/about/prevent-bites.html.