Causes of summer fever/summer colds and when to see a doctor
目次
"I have a fever even though it's summer," "my throat hurts and I feel sluggish," "I feel unwell after turning on the air conditioner"—from the end of the rainy season to early autumn, we see a rapid increase in patients coming to our clinic with these symptoms.
Summer fevers are caused by different viruses than winter colds. In this season, as more enclosed spaces with air conditioning and closed windows become common, viruses tend to linger indoors. Summer-specific infections such as pharyngoconjunctival fever (pool fever), streptococcal infection, herpangina, coronavirus infection, and coinfection of influenza and coronavirus (so-called "Inco-Flu") are particularly prevalent.
This page explains why fevers increase in summer, the characteristics of major summer infections, when to seek medical attention, and the tests and treatments available at our clinic.
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Accurate diagnosis of the cause with rapid tests (influenza, COVID-19, streptococcus)
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Prescription of medication and symptomatic treatment tailored to your symptoms
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Advice on preventing infection for family and workplace
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Walk-ins welcome, same-day appointments OK | Open daily from 9 AM
👉 If you have a persistent fever in summer or a sore, swollen throat, please visit us first.
👉 Walk-ins are also welcome. Please feel free to consult us.
Why Infections Increase in Summer | The Relationship with Air Conditioning and Enclosed Spaces
"In summer, it's hot, so people close windows and turn on air conditioning"—this is one of the major factors contributing to the spread of infections in summer.
① Viruses linger in enclosed spaces
In closed rooms, viruses contained in sneezes, coughs, and breath of infected individuals are not ventilated and continue to linger in the air. As viruses spread throughout the room with the air conditioner's breeze, the risk of infection increases simply by being in the same space. Enclosed spaces with air conditioning, such as workplaces, schools, trains, and restaurants, become breeding grounds for infection.
② Mucosal dryness and decreased immunity due to air conditioning
Inhaling cold air from air conditioners for extended periods lowers the surface temperature of the mucous membranes in the throat and nose, reducing local blood flow and the activity of immune cells. Additionally, indoor humidity often drops below 40% when air conditioners are in use, leading to reduced mucus secretion. This weakens the barrier function of the mucous membranes, making it easier for viruses to invade.
③ Disruption of autonomic nervous system due to indoor-outdoor temperature differences
Repeated abrupt temperature changes from outdoors above 35°C to air-conditioned rooms in the 20s°C disrupt the balance of the autonomic nervous system. This impairs thermoregulation and weakens immunity, leading to a prolonged state of susceptibility to viral infections. This is also why "summer fatigue" and infections often coincide.
④ Summer viruses are less susceptible to alcohol disinfection
While influenza viruses and winter coronaviruses, which cause winter colds, are effectively disinfected by alcohol, enteroviruses (herpangina, hand-foot-and-mouth disease), which are major causes of summer infections, have high resistance to alcohol. Handwashing with soap and running water is the most effective preventive measure.
Major Summer Infections | Types, Characteristics, and How to Differentiate Them
Fevers in summer can have multiple causes. Since the causes and treatments differ even for similar symptoms, accurate diagnosis is crucial.
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Disease Name |
Main Symptoms |
Cause/Transmission Route |
Treatment |
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Pharyngoconjunctival Fever (Pool Fever) |
Three major symptoms: high fever of 39-40℃, throat swelling, and eye redness (conjunctivitis). Eye symptoms often start in one eye |
Adenovirus. Droplet/contact infection. Previously common from pool water, now mainly everyday contact |
No specific drug. Antipyretic/symptomatic treatment. Exclusion from school/work (2 days after symptoms disappear) |
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Streptococcal Infection (Streptococcal Pharyngitis) |
Sudden high fever, severe sore throat, white pus on tonsils. Little cough/runny nose. May be accompanied by rash (scarlet fever) |
Group A Streptococcus (bacteria). Droplet/contact infection. Peak in spring-summer and winter |
Antibiotics (penicillin-based) effective. 10-day course usually. Untreated, risk of kidney inflammation/heart inflammation complications |
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Herpangina |
High fever of 38-40℃, blisters/ulcers in mouth (around uvula), severe sore throat. Common in infants/young children |
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Access & Opening Hours
From ItabashiJR埼京線で1駅2分
From AkabaneOne stop, four minutes on the JR Saikyo Line
From IkebukuroJR埼京線で約10分
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