Furnace Season

Small Hinges No. 02 · November 2026 · Real change you can feel, one small hinge at a time.

Sometime this fall, the furnace came on.

You smelled it. That warm, dusty smell on the first cold night. Then the windows closed, and most of them will stay shut until April.

Here is what changed, and why colds love it.

Why November is different

Cold air holds very little water. When the furnace heats that air, it does not add any water. It just makes dry air warm. By the middle of winter, the air in many Canadian homes is drier than a desert afternoon.

Colds like dry air, for two reasons. Germs that float out of a cough stay infectious far longer in dry air. And your own nose, your first line of defence, works worse when it is dry and cold.

And now we are all inside together, breathing the same air, for five months.

You cannot dodge every cold. But the odds are not fixed. Here are the three hinges from this month's email, with the science behind them, and then four more from the video.

Watch

Preparing for the cold-season battle, 90 seconds. All seven defences, in the order of the proof.

01 · Keep the air near 40 percent

Humidity is how much water is in the air. A lab at the US CDC coughed flu germs into the air of a sealed room, using a machine, and measured how many could still infect an hour later.

In dry air, like most heated Canadian homes in January, about 3 in 4 germs were still infectious. When the room's humidity was above 40 percent, it was about 1 in 5.

That was a lab simulation, not a count of real colds. But it fits what doctors have long seen: dry winter air and cold season arrive together.

How: a small digital humidity gauge costs about 15 dollars at the hardware store. Put it on the kitchen counter. If it reads low, a humidifier brings it up. Health Canada's comfortable indoor range is 30 to 50 percent. One warning sign to watch: if your windows fog or drip, the air is too wet, and that invites mould. Turn the humidifier down.

02 · Pull the scarf over your nose

Your nose fights germs with tiny decoys. When a virus lands in your nose, your nose releases billions of tiny particles that look like the cells the virus wants to attack. The virus grabs the decoys instead of you.

Researchers at Harvard's Mass Eye and Ear measured what cold weather does to that defence. Fifteen minutes of winter air cooled the inside of the nose by about 5 degrees. That small drop cut the decoys by almost half.

Honest note: this was a lab finding about the mechanism. It did not count who caught colds. But a scarf costs nothing, and it keeps the air you breathe warm and a little damp before it reaches your nose.

How: when you head out into the cold, pull the scarf up over your nose, not just around your neck.

03 · Six hours, at least

Sleep is part of your immune system. Researchers measured the real sleep of 164 healthy adults for a week, with motion sensors on their wrists, not diaries. Then, with the volunteers' agreement, they put a cold virus directly into each person's nose.

People who had been sleeping six hours or less were about four times as likely to get sick as people who slept more than seven. Shorter sleep, in the week before the virus arrived, made the body easier to infect.

How: treat sleep like part of your cold defence, especially in the two weeks after the clocks change. If sleep itself is the problem, our free guide can help: The Ultimate Sleep Report, nine pages by Brad King.

Four more, from the video

The three hinges above are this month's email. The video covers four more. Here they are, in order of how good the proof is.

04 · Wash your hands. Twenty seconds. The least glamorous defence has the biggest trials. A Cochrane review pooled hand-washing studies covering more than 50,000 people. Hand hygiene programs cut respiratory infections by about 14 percent. Soap, twenty seconds, especially after coming home and before eating.

05 · Keep moving. Here is the honest version. In trials, regular moderate exercise, like a brisk half-hour walk most days, did not stop people from catching colds. But the colds they caught were milder, and across the season they spent about two fewer days feeling sick. Milder and shorter is worth a walk.

06 · Top up your vitamin D. From November to February, the sun stops making vitamin D in your skin. October's issue showed why. An analysis of 25 trials found that taking vitamin D regularly cut respiratory infections, with the biggest benefit in people who were low to begin with. A larger 2021 update found a smaller but still real edge. Take it daily, with a meal that has fat in it.

07 · Have a plan for the day a cold gets through. That plan is below.

The Winter Cupboard

Three supplements with a real winter case. Good information only. Buy them wherever you like.

Vitamin D3, with K2. The case is above. A daily D3 supplement helps maintain immune function through the dark months. Take it with the fattiest meal of the day. Many D3 drops come paired with vitamin K2, which helps keep bones strong.

Zinc, all winter. Your immune system needs zinc to work. In a year-long trial, adults aged 55 to 87 who took zinc every day had about one fifth the infections of those on a placebo. Seventeen of the twenty-four people on zinc went the whole year with no infection at all. A small daily zinc supplement helps maintain immune function. Keep it under 40 mg a day, Health Canada's adult limit.

Fulvic acid, from shilajit. Shilajit contains a fascinating ingredient called fulvic acid. Winter is hard on bones and joints: in a six-country European study, two in three older adults with arthritis said the weather worked against them. In a 48-week trial, women past menopause with thinning bones took a daily shilajit extract, rich in fulvic acid. They held on to bone density the placebo group kept losing, and the higher dose held best. A daily shilajit supplement helps support healthy bones.

An old kitchen remedy: clove and thyme

Your grandmother may have put a few drops of clove or thyme oil in a bowl of hot water and leaned over the steam. Here is what we know, and what we don't.

Why these two together. Thyme and clove fight germs in different ways. Thyme's main weapon is a compound called thymol. Clove's is eugenol. They attack a germ's outer wall from two directions, which works better than more of one thing. In a 2022 Italian lab study, thyme and clove oil together beat either oil alone, and the pair worked best as a vapour. That is the steam bowl, in a dish. (That study used food germs, not cold germs.)

Against cold-season germs. In 2018, scientists in Hungary tested seven oils against the germs behind sore throats, ear infections and bronchitis. Cinnamon and thyme were the strongest, then clove. Thyme worked as a vapour too.

In people. In a 2023 trial in Turkey, 140 hospital patients with COVID breathed thyme oil three times a day for five days. They had less cough and less shortness of breath than the group that did not. The catch: the patients knew which group they were in, so part of that may be the comfort of a warm steam.

What no one has shown yet. There is no trial of clove and thyme together for the common cold. So we can say the oils fight germs in a dish, and that the steam feels good. We cannot say it will stop or shorten your cold.

If you try it, do it safely.

• Two or three drops in a bowl of hot, not boiling, water. Towel over your head, eyes closed, five minutes.
• Never swallow essential oils. Never put them on skin without a carrier oil.
• Keep clove oil away from children. Even a small swallowed amount can be dangerous for a child.
• Keep both oils away from pets, especially cats.
• The gentle version: thyme in a cup of tea, with honey. Thyme as a drink has real trial evidence for cough. In a German study of 361 adults with bronchitis, a thyme-and-ivy syrup cut coughing fits by 69 percent, against 48 percent on a placebo.

If a cold gets through anyway

None of these will stop a cold. Each one has some proof it can make a cold shorter or easier.

A hot drink with honey. In a small study, a hot drink eased a runny nose, cough and sore throat right away. A review of 14 trials found honey calmed a cough better than usual cold remedies. Any tea you like works; thyme, ginger and peppermint are old favourites. Never give honey to a baby under one.

Make it Canadian honey. No study says Canadian honey works better, and we won't pretend otherwise. But if honey is going in your tea all winter, it may as well come from a Canadian beekeeper. Find one near you at buycanadianhoney.ca, with 359 producers listed by province.

South African geranium (PelaForce), at the first sign. A plant remedy made from the root of a South African geranium. A Cochrane review of eight trials found it eased bronchitis in adults and children, with evidence a notch stronger than zinc's. It also helped sinus infections and colds, with weaker proof. Side effects were mild. Health food stores carry it in natural cold formulas.

Zinc lozenges, at the first sniffle. These are different from daily zinc. Started early, they can cut a cold by about two days; a review of 34 trials found that. What it did not find is zinc stopping a cold from starting. Lozenges are for a few days, not all winter, because the lozenge doses run above Health Canada's daily limit.

The furnace-season checklist

Everything on this page, on one page. Print it and put it on the fridge.

⬇ Download the checklist (PDF)🖨 Print this page’s checklist

The research behind this issue

• Humidity: Noti JD, Blachere FM, McMillen CM, et al. High humidity leads to loss of infectious influenza virus from simulated coughs. PLoS One. 2013;8(2):e57485. US CDC/NIOSH. Infectivity 70.6–77.3% at relative humidity ≤23%, vs 14.6–22.2% at ≥43%. Lab simulation. Health Canada's indoor comfort range: 30–50%.
• Cold nose: Huang D, Taha MS, Nocera AL, et al. Cold exposure impairs extracellular vesicle swarm–mediated nasal antiviral immunity. Journal of Allergy and Clinical Immunology. 2023;151(2):509–525. Mass Eye and Ear / Harvard. 15 minutes at 4.4°C cooled the nose ~5°C and cut extracellular vesicles ("decoys") by ~42%. Mechanism study only.
• Sleep: Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally assessed sleep and susceptibility to the common cold. Sleep. 2015;38(9):1353–1359. 164 adults, wrist actigraphy, then rhinovirus exposure. Under 6 hours: roughly four times the odds vs more than 7.
• Hand-washing: Jefferson T, et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. Cochrane Database of Systematic Reviews. 2023;1:CD006207. Hand hygiene: ~14% fewer acute respiratory infections (9 trials, 52,105 people; moderate certainty).
• Exercise: Grande AJ, et al. Exercise versus no exercise for the occurrence, severity, and duration of acute respiratory infections. Cochrane Database of Systematic Reviews. 2020;4:CD010596. 14 trials, 1,377 adults. No fewer colds; lower severity (moderate certainty) and about 2.2 fewer symptom-days over follow-up (low certainty).
• Vitamin D: Martineau AR, et al. Vitamin D supplementation to prevent acute respiratory tract infections. BMJ. 2017;356:i6583. 25 trials, 11,321 people; biggest effect in the deficient. Update: Jolliffe DA, et al. Lancet Diabetes & Endocrinology. 2021: smaller but still protective overall effect.
• Zinc, daily: Prasad AS, et al. Zinc supplementation decreases incidence of infections in the elderly. American Journal of Clinical Nutrition. 2007;85(3):837–844. Health Canada monograph: zinc "helps to maintain immune function"; adult upper limit 40 mg/day.
• Zinc lozenges: Nault D, et al. Zinc for prevention and treatment of the common cold. Cochrane Database of Systematic Reviews. 2024;5:CD014914. 34 trials: no prevention; colds about two days shorter when started early (low certainty).
• Bones and weather: Timmermans EJ, et al. Self-perceived weather sensitivity and joint pain in older people with osteoarthritis in six European countries. BMC Musculoskeletal Disorders. 2014;15:66. Shilajit: Pingali U, Nutalapati C. Shilajit extract reduces oxidative stress, inflammation, and bone loss to dose-dependently preserve bone mineral density in postmenopausal women with osteopenia. Phytomedicine. 2022;105:154334. 60 women, 48 weeks, extract standardized to >50% fulvic acids.
• Hot drink: Sanu A, Eccles R. Rhinology. 2008;46(4):271–275. Honey: Abuelgasim H, et al. BMJ Evidence-Based Medicine. 2021;26(2):57–64. 14 trials.
• Pelargonium: Timmer A, et al. Pelargonium sidoides extract for treating acute respiratory tract infections. Cochrane Database of Systematic Reviews. 2013;10:CD006323.
• Clove & thyme: Sateriale D, et al. Microorganisms. 2022 (synergy, vapour phase) · Ács K, et al. BMC Complementary and Alternative Medicine. 2018 · Öner U, Cengiz Z. Explore. 2023 (unblinded) · Kemmerich B, et al. Arzneimittelforschung. 2006 (thyme-and-ivy syrup, 361 adults).

This article is for education. It is not medical advice. Talk to your health care practitioner before changing your supplements, especially if you are pregnant or take medication.

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