Global average temperatures have soared in 2024, surpassing records set just last year. Extreme heat poses numerous health risks, some of which are visible on our skin. Understanding how heat affects your skin can help you take measures to prevent or ease heat rash, eczema, rosacea, the discoloration of melasma, and many other skin conditions sparked or worsened by high temperatures.

Heat waves can provoke or worsen several skin conditions.

During heat waves, levels of environmental pollutants like ozone and particulate matter can rise. And reactions between these pollutants, heat, and UV radiation spawn secondary pollutants such as peroxyacetyl nitrates (PANs). Pollutants like these can irritate the skin and contribute to inflammation through oxidative stress and DNA damage, so inflammatory conditions such as eczema and rosacea may worsen.

High temperatures compromise the effectiveness of certain medications. For instance, EpiPens, which are crucial for managing life-threatening allergic reactions, can lose their potency when exposed to high temperatures. Check the instructions on all of your medicines to see which ones should be stored in a cool, dry place or refrigerated. If you're not sure which medicines might be affected by heat, talk to your pharmacist or doctor.

Retinoids in skin care products, antibiotics taken for acne, and immunomodulators for autoimmune diseases can make skin more susceptible to sun damage. This can lead to severe sunburns or rashes known as photodermatoses. If you experience this, contact your health care team for advice.

Source: Harvard Health Publishing

Animals renowned for their outstanding night vision include owls, cats, tarsiers (a tiny primate in Southeast Asia) — and even the dung beetle.

But humans? Not so much.

Over time, many people suffer from night blindness, also known as nyctalopia. This condition makes seeing in dim or dark settings difficult because your eyes cannot adjust to changes in brightness or detect light.

Night blindness is especially problematic and dangerous when driving. Your eyes cannot adjust between darkness and the headlights of oncoming vehicles, other cars may appear out of focus, and your depth perception becomes impaired, which makes it difficult to judge distances.

Night blindness also may affect your sight at home by making it hard for your vision to quickly adjust to a dark room after turning off the lights. "This can cause people to bump into furniture or trip and suffer an injury," says Dr. Isabel Deakins, an optometrist with Harvard-affiliated Massachusetts Eye and Ear.

The ability to see in low-light conditions involves two structures in the eye: the retina and the iris.

The retina, located in the back of the eye, contains two types of light-detecting cells called cones and rods. The cones handle color vision and fine details while the rods manage vision in dim light.

The iris is the colored part of your eye. It contains muscles that widen or narrow the opening of your pupil to adjust how much light can enter your eyes.

If your irises don't properly react, the pupils can dilate and let in too much light, which causes light sensitivity and makes it hard to see in bright light. Or your pupils may remain too small and not allow in enough light, making it tough to see in low light.

Night blindness is not a disease but a symptom of other conditions. "It's like having a bruise on your body. Something else causes it," says Dr. Deakins.

Several conditions can cause night blindness. For instance, medications, such as antidepressants, antihistamines, and antipsychotics, can affect pupil size and how much light enters the eye.

Eye conditions that can cause night blindness include:

However, one issue that raises the risk of night blindness that you can't control is age. "Our eyes react more slowly to light changes as we age, and vision naturally declines over time," says Dr. Deakins.  "The number of rods in our eyes diminish, pupils get smaller, and the muscles of the irises weaken."

If you notice any signs of night blindness, avoid driving and get checked by an eye care specialist like an optometrist or ophthalmologist. An eye exam can determine if your eyeglass prescription needs to be updated.

"Often, a prescription change is enough to reduce glare when driving at night," says Dr. Deakins. "You may even need separate glasses with a stronger eye prescription that you wear only when driving at night."

Adding an anti-reflective coating to your lens may help to cut down on the glare of the headlights of an oncoming car. However, skip the over-the-counter polarized driving glasses sold at many drug stores. "These may help cut down on glare, but they don't address the causes of night blindness," says Dr. Deakins.

An eye exam also will identify glaucoma or cataracts, which can be treated. Glaucoma treatments include eyedrops, laser treatment, or surgery. Cataracts are corrected with surgery to replace the clouded lens with an artificial one. Your eye care specialist can also help identify dry eye and recommend treatment.

Ask your primary care clinician or a pharmacist if any medications that you take may cause night blindness. If so, it may be possible to adjust the dose or switch to another drug.

You also can take steps to make night driving safer. For example:

Harvard Health Publishing