For most people, winter means bundling up in layers, cranking up the heater, and avoiding the outdoors whenever possible. Yet, some individuals seem completely unfazed by freezing temperatures, comfortably strolling through snow in light jackets or even short sleeves. This striking difference raises an intriguing question: why are some people naturally less sensitive to cold? Is it a matter of physical conditioning, genetic predisposition, or something else entirely?

The Physiology of Cold Resistance

Human tolerance to cold is a complex interplay between biological and environmental factors. At the physiological level, our bodies respond to cold through mechanisms like shivering, vasoconstriction (narrowing of blood vessels), and increased metabolic heat production. However, the efficiency of these mechanisms varies significantly from person to person. Those who handle cold better often exhibit more efficient brown adipose tissue (BAT) activity. Unlike white fat, which stores energy, brown fat burns calories to generate heat—a process called thermogenesis. Studies show that individuals with higher amounts of active brown fat tend to feel less cold in chilly environments.

Another factor is muscle mass. Muscles play a crucial role in generating body heat, which is why people with greater muscle density often report higher cold tolerance. Additionally, differences in blood circulation can influence how cold someone feels. People whose bodies prioritize keeping core organs warm over maintaining peripheral warmth might have colder hands and feet but remain relatively comfortable overall.

Genetic Factors Behind Cold Tolerance

Genetics undeniably play a role in how we perceive and withstand cold. Certain populations, such as the Inuit of the Arctic or the Sherpas of the Himalayas, have evolved genetic adaptations that enhance their ability to thrive in frigid climates. Research has identified specific gene variants linked to cold resistance, including those affecting thyroid function, which regulates metabolism, and UCP1, a protein crucial for brown fat activation.

One notable example is the ACTN3 gene, often referred to as the "speed gene," which has been associated with improved cold adaptation in some athletes. Another gene, TRPM8, codes for a receptor that detects cold temperatures. Variations in this gene can alter a person’s sensitivity to chilly environments. While these genetic differences don’t entirely explain why one person shivers at 50°F while another remains unfazed, they do contribute to the broader picture of innate cold resistance.

The Role of Acclimatization and Lifestyle

Beyond genetics, repeated exposure to cold can train the body to handle lower temperatures more effectively. This phenomenon, known as cold acclimatization, is why individuals who live in colder regions or frequently engage in winter sports often develop a higher tolerance over time. The body adapts by improving blood flow regulation, increasing brown fat activity, and even altering how the brain perceives temperature signals.

Lifestyle choices also come into play. Regular exercise, particularly high-intensity workouts, can boost metabolism and improve circulation, both of which help in retaining body heat. Diet matters too—foods rich in healthy fats and proteins provide the necessary fuel for thermogenesis. Even mental conditioning, such as meditation or breathing techniques practiced by Wim Hof (famously known as "The Iceman"), can influence how the body responds to cold stress.

When Cold Tolerance Becomes a Concern

While some degree of cold resistance is normal, extreme insensitivity to cold can sometimes signal underlying health issues. Conditions like hypothyroidism, anemia, or Raynaud’s disease can impair the body’s ability to regulate temperature, leading to abnormal reactions to cold. Conversely, those with exceptionally high cold tolerance should still be cautious, as prolonged exposure to freezing temperatures can lead to frostbite or hypothermia, even if symptoms aren’t immediately felt.

Understanding the balance between genetic predisposition and environmental adaptation helps explain why some people are naturally less affected by cold. Whether it’s a combination of active brown fat, favorable genes, or a lifestyle that embraces the chill, the science behind cold tolerance continues to fascinate researchers. For the rest of us, it might just be a reminder to invest in a good winter coat.