A newborn can't regulate their own temperature. Their thermoregulatory system is, at birth, both developmentally limited and poorly differentiated — which means they can't cool themselves down the way older children and adults do (Osilla EV et al., StatPearls, 2023). They rely almost entirely on their environment: the clothes they're wearing, the air around them, and the adults paying attention.
This doesn't mean summer with a newborn is complicated. It means it requires a little more active management than most people expect.
The Temperature Problem
Newborns have a larger surface-area-to-mass ratio than older children — a ratio that declines roughly 28% across the first year of life (van de Kamp and Daanen, IJERPH, 2025). In moderate temperatures, this actually helps with heat dissipation. In extreme heat, it becomes a liability: the same physical characteristic that helps them stay cool in mild weather accelerates heat absorption when the environment is very warm.
Their sweating capacity is also limited. Where adult sweating is an efficient, rapid cooling mechanism, infant sweat output per gland is lower — and a greater proportion of what is produced evaporates rather than running off the skin (van de Kamp and Daanen, 2025). The system functions, but more slowly and with less reserve.
The practical result: a newborn can become uncomfortably or dangerously hot faster than an adult would, and with less obvious warning.
The recommended sleeping environment temperature for a newborn is 16–20°C. In a Danish summer, this is usually straightforward. During a heat spell, it requires thought.
Sun Exposure
Newborn skin is not ready for direct sunlight. According to Sundhedsstyrelsen (SST), babies under 6 months should be kept out of direct sun entirely during peak UV hours — 11am to 3pm — and should have adequate shade at all other times (SST, Faktaark om solbeskyttelse, 2025).
The reasoning is simple: newborn skin has very little melanin and burns faster than adult skin, often before it looks pink.
Sunscreen under 6 months: SST advises against sunscreen for babies under 6 months except as an absolute last resort — not because sunscreen is toxic, but because shade and clothing are more reliable and require no reapplication. A UV-rated hat and a lightweight long-sleeved layer will block more UV than any cream.
What "shade" actually means: A pram canopy is not the same as shade. Fabric canopies can let through more UV than they appear to, and draping a blanket over the hood to block sunlight creates a heat trap. A UV-rated parasol, positioned between the sun and the baby, is more reliable.
After 6 months, a children's mineral sunscreen (minimum SPF 30) on exposed skin that can't be covered is appropriate.
Signs of Overheating
The hands and feet are often cooler than the rest of the body and will mislead you. The neck and chest are the reliable indicators. A warm, slightly sweaty chest means the baby is too hot. A warm but dry neck is usually fine.
Signs that require action:
- Rapid breathing
- Flushed skin with visible sweating
- Restless and unable to settle despite feeding
- Unusually quiet or limp
If any of these appear alongside a hot environment, cool the baby down immediately: move to shade or an air-conditioned space, remove a layer, offer a feed. If you are unsure, call your sundhedsplejerske or 1813.
Sleep in the Heat
Heat disrupts sleep. A baby who was settling reasonably well may become harder to settle when the room is warm, and night wakings may increase. This is not a sleep regression — it's a temperature problem.
According to SST sleep guidance, the appropriate clothing for a sleeping baby changes significantly with room temperature (SST, Anbefalinger for søvnlængde, 2024):
- Above 22–23°C overnight: a single light babygrow without a sleeping bag
- Above 25°C: a nappy and a thin muslin may be sufficient
The temptation when a baby is waking more in the heat is to add layers. This is the wrong direction. Night wakings in summer are often a sign the baby needs less on, not more.
Airflow helps: A fan moving air around the room — not pointed directly at the baby — makes a meaningful difference. Cross-ventilation if possible. Keeping curtains closed during the day reduces solar heat gain before bedtime.
Getting Outside
Pram: aim for before 11am or after 4pm. A parasol rather than a blanket over the hood. Check that air can circulate around the baby — some footmuffs and pram inserts are extremely warm and inappropriate in summer.
Baby carriers: A structured carrier with padding retains heat for both you and the baby. A woven or mesh carrier breathes better. Watch for signs of overheating during outings; keep them shorter in peak heat.
Car seats: A car seat left in a warm car, or one that's been in direct sunlight, gets substantially hotter than the air temperature — hot enough for the metal buckle hardware to cause burns. Before placing a baby in any car seat that's been sitting in the sun or a warm car, check the metal parts with the back of your hand or inner forearm. A towel or car seat cover over the seat while parked reduces heat buildup.
Never leave a baby in a parked car, even briefly, even with a window cracked.
Hydration
Breastfed babies under 6 months do not need extra water in hot weather. Breastmilk adjusts its composition to provide adequate hydration — additional water at this age can interfere with feeding and, in larger quantities, cause electrolyte imbalance (SST, Faktaark om solbeskyttelse, 2025).
Formula-fed babies similarly do not require water supplements in standard Danish summer temperatures, though responding to cues for more frequent feeds in the heat is appropriate.
Small amounts of water alongside food are appropriate from 6 months, once solids have started.
What People Overcorrect On
The summer advice has a way of making a walk to the corner shop feel like a disaster preparedness exercise.
A brief moment of sun exposure while moving from pram to indoors is not harmful. A hat and a shaded pram cover most situations. You don't need to stay inside all day.
A baby who is slightly warm but feeding well, alert, and settled is fine. The signs described above are the ones that matter. Warm hands are not the ones that matter.
Most Danish summers involve a handful of genuinely hot days. The rest is mild and manageable with basic precautions.
Frequently Asked Questions
Can I put sunscreen on my newborn?
SST advises against sunscreen for babies under 6 months — not because it's toxic, but because shade and UV-rated clothing are more effective and reliable. Sunscreen can be used after 6 months: a children's mineral SPF 30 on exposed skin.
How do I know if my newborn is too hot?
Check the neck and chest — not the hands or feet. A warm, sweaty chest means too hot. Rapid breathing, flushed skin, or unusual limpness requires you to cool them down immediately and seek advice if it doesn't resolve quickly.
Can I take my newborn outside in summer?
Yes. Avoid peak UV hours (11am–3pm), keep them shaded, use a hat and light clothing rather than sunscreen. Early morning and late afternoon are the easiest times.
Should I give my newborn water in the heat?
No — not before 6 months. Breastmilk or formula provides all the hydration a baby needs. Offer feeds more frequently if the baby seems to want them.
What temperature should the room be for a sleeping newborn in summer?
16–20°C is ideal. Above 22°C, reduce bedding to a single light layer. Above 25°C, a nappy and thin muslin may be enough. Check the chest — not the hands — to gauge temperature.
Sources
- Osilla EV et al. Physiology, Temperature Regulation. StatPearls, 2023.
- van de Kamp E, Daanen H. Narrative Review on Infants' Thermoregulatory Response to Heat. IJERPH, 2025.
- Sundhedsstyrelsen. Faktaark om solbeskyttelse. 2025.
- Sundhedsstyrelsen. Anbefalinger for søvnlængde. 2024.