Is It Safe to Take My Newborn Out on a Hot Day?

I’m a first-time mom with a two-month-old. We’re an outdoorsy family, and it’s starting to get into the 90s where we live. I saw that the American Academy of Pediatrics says to avoid taking babies outside when the heat index is greater than 90 degrees. I’ve seen other sources say to stay inside if the outdoor temp is over 80! Some say to dress babies in short sleeves (to prevent overheating), others say long sleeves (to limit sun exposure). How do we safely have fun outside with our baby this summer? What are the precautions and risks for sun exposure vs. overheating that we should actually take into consideration?
—Desperately Seeking Sun

One time, when my daughter was four months old, we were on an ill-timed vacation someplace extremely hot, and my husband and I got lost on a walk with the baby. In the pictures I have, I’m soaked in sweat, with the baby strapped to me in a Bjorn carrier and happily sleeping under a hat. My point being: if you take your baby out in the heat, don’t get lost.

Your question on sunscreen is easier to answer, and I wrote a little more about it in the second question here. The bottom line is that for young babies — or anyone — it’s better to get sun protection through clothing than sunscreen. But there isn’t any special reason babies cannot have a small amount of sunscreen on exposed skin if necessary.

In terms of heat, the primary issue is that babies do not sweat as much as adults and get hot more quickly. They are therefore more prone to overheating, heat stroke, and dehydration. My sense is that a source of a lot of the caution is the relative tolerance of babies (or kids) versus adults. As in: just because you are comfortable, doesn’t mean the baby will be.

However, there isn’t anything I can see in the data that would suggest a “rule” about when you can and cannot take your infant outside. Researchers in the 1980s ran experiments on how babies react to heat, showing that babies have some ability to adjust to heat. (Also, the fact that these experiments were ethical suggests that some heat exposure is not too dangerous.)

It’s important to be aware of the possibilities of overheating and dehydration and react to them. Infants may need more fluids (either more breastfeeding or more formula or, for an infant over six months, water). As babies get hot, they can get very flushed — this may be a sign to go inside. And, as for anyone, if you can do your outside time earlier in the morning or later in the afternoon, that’s better.

On the whole, awareness of these issues and sensitivity to them is the key, rather than a rule about not taking babies outside under a particular cutoff temperature.