Winter in Phoenix: What Actually Goes Around, and What the Season Is Good For

Almost everything written about winter health assumes winter is the problem. Bundle up, fight the cold, get through it. Here, winter is the best six months of the year — and treating it as something to endure means wasting the one stretch when being outside is easy.

So this page does two things. It covers what genuinely circulates in a Phoenix winter, which is real and is not caused by the weather. And it makes the case for using October to April rather than surviving it.

What actually goes around, and why

The cold does not cause colds. Nor does going out with wet hair, or sitting near a draught. Respiratory illness is caused by viruses, and the reason they spread in winter everywhere — including here — is behaviour, not temperature. We go indoors, close the windows, turn off the air conditioning, and spend more time in the same air as other people. Schools are in session. Holidays put extended families in one room.

Phoenix gets a full respiratory season and the desert does not exempt anyone from it:

Influenza, which here runs later and longer than the national coverage suggests — often still climbing in February and March, well after everyone has stopped thinking about it. That is also why a flu shot in December is still worth getting in Arizona. Our flu page covers telling it from a cold, and the 48-hour window that matters.

RSV, which is a minor cold in most people and a serious illness in babies and older adults.

COVID-19, which has not settled into a neat season.

Ordinary colds, several in a row through a school year — which is how one lingering cough gets mistaken for six illnesses.

Strep throat, which is bacterial and peaks in school-age children in these months. A sore throat with fever and no cough or runny nose points that way.

Norovirus, the winter vomiting bug, which spreads through surfaces and hands and is not killed by alcohol gel. Soap and water for this one.

What actually helps: handwashing, staying home while feverish, the flu shot and whatever else is current, and not sharing cups and utensils. Vitamin C does not prevent colds. Vitamin D is worth a word — deficiency is common here despite the sun, precisely because sensible people avoid the sun for eight months, and it is a reasonable thing to ask about rather than to self-prescribe.

The Arizona winter things nobody mentions

Our second allergy season. Autumn brings a genuine pollen run here, and winter rain drives early spring blooming. A child who “catches a cold” every February is quite often not catching anything — itchy eyes, sneezing, a clear runny nose and no fever point at allergy, not infection. Our allergy page covers the local calendar, which is not the national one.

Valley fever peaks in the cooler, drier months, after the monsoon has stirred the soil. It presents as a cough with fatigue lasting weeks and it is regularly diagnosed only after two or three courses of antibiotics have failed, because it looks exactly like a chest infection that will not clear. Antibiotics do nothing to a fungus. If a cough is still there after three weeks, say so.

Dust and wind without any bloom. Construction, wind events and dry ground put fine particulate in the air on days when nothing is flowering, and the cough that follows is irritant rather than infectious.

Cold snaps catch people out precisely because they are rare. Nights near freezing happen, houses here are built to shed heat rather than hold it, and space heaters are the fire and carbon monoxide risk of the season. A carbon monoxide alarm is worth having even in a mild climate — a gas furnace used for six weeks a year is a gas furnace that has not been checked.

And the population that changes. Winter visitors arrive, households gain grandparents for months, and the number of older adults in the Valley goes up considerably. That matters for anyone with a new baby at home: the adult pertussis and flu situation in the visiting relatives is a real question, not a fussy one. Our whooping cough page explains why most infected babies catch it from an adult at home.

What this season is actually for

This is the part the national template cannot write.

Build the exercise habit now. From October to April this is close to the best climate in the country for walking, cycling, hiking and being outdoors with children. A habit started in November is the one that survives into summer; a habit started in June does not exist. If you have been meaning to start something, the weather has stopped being your excuse for six months.

It is the best sleeping weather of the year. Nights actually cool down, which matters because body temperature has to fall a little for sleep to begin. If summer has left you short on sleep, this is when to reset the schedule — our insomnia page covers how, and the fixed wake time is where to start.

Get the appointments done. Blood pressure, cholesterol, blood sugar, a skin check, the flu shot, the dental visit, whatever has been drifting. There is a practical reason to do it now rather than in January: if your insurance deductible resets on 1 January, the work you have already paid toward this year is worth using before it disappears. That is a real financial argument and it is the one nobody makes to you.

And do the sun protection anyway. A 70-degree February day in Arizona still carries substantial UV, and winter is when people here stop bothering — hiking for three hours in January without sunscreen is an ordinary local sunburn. Our skin cancer page covers why that matters more here than almost anywhere.

Call us if

• A fever lasting more than three days, or one that goes and comes back
• Symptoms that improve and then get worse again — the pattern that suggests a second infection on top of the first
• A cough lasting more than three weeks
• Any difficulty breathing, or breathing that looks like hard work
• A sore throat with fever and no cough or runny nose
• Any fever in a baby under one month, which is an emergency at any time of year
• A child with asthma needing their reliever more than usual — winter viruses are one of the most reliable triggers there is
• Vomiting or diarrhoea with signs of dehydration
• You are due for something on the list above and have not got round to it

Sources

2. Pertussis — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/001561.htm
55. Carbon Monoxide Poisoning — MedlinePlus topic page, U.S. National Library of Medicine (summary from the Centers for Disease Control and Prevention). https://medlineplus.gov/carbonmonoxidepoisoning.html
59. Areas with Valley Fever — Centers for Disease Control and Prevention. https://www.cdc.gov/valley-fever/areas/index.html
60. Symptoms of Valley Fever — Centers for Disease Control and Prevention. https://www.cdc.gov/valley-fever/signs-symptoms/index.html

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