In recent years, while the climate has shifted, one thing has remained the same. Walking through the streets of Toronto, you’ll find an assortment of attire, ranging from people dressed like Eric Cartman from South Park to others who wear a sweatshirt and call it a day.

Which begs the question, why do some people get colder than others? Temperature in our bodies depends on a number of biological factors. Interwoven mechanisms in our body maintain internal temperature — beginning from the skin where nerves lie in wait for a change in the outside environment. Upon detection, the nerves send signals to the hypothalamus, which initiates a number of defence operations. 

Common responses to feeling cold are shivering and vasoconstriction. Shivering increases heat generation in our bodies and vasoconstriction reduces heat loss by physically narrowing blood vessels — this constriction can lead to the pallor of the skin in our extremities. In certain instances, this pallor is indicative of more serious issues such as Raynaud’s disease. 

While our bodies employ the same mechanisms, perceptions of cold weather can vary from person to person. This variability is due to a cohort of different physiological and psychological characteristics. The hypothalamus triggers the same key responses in every person but its assessment of when it deems a response is fit is unique to the physical characteristics of each individual.

Body fat is the most ubiquitous characteristic. It is fairly well known that more fat results in greater insulation. In particular, it is the subcutaneous fat — the layer of fat directly beneath our skin — that provides the best resistance to cold. Though most magazines and health gurus tout fat as undesirable, it plays an integral role in maintaining sufficient heat to bear the unrelenting cold we’ve come to face annually. 

Cold resistance also varies across sexes. Men’s and women’s bodies differ in subcutaneous fat, surface area, and hormones, all of which impact cold perception. For example, a woman will probably typically feel colder than a man due to an overall greater surface area and smaller body mass of the woman’s body.

Shorter time scale fluctuations in our bodies can also lead to day-to-day differences in our responses to outside temperatures. Fluctuations in hormones during the menstrual cycle, for women, and in testosterone levels, for men, change perceptions of temperature. For example, testosterone inhibits a key cold receptor, reducing sensitivity to lower temperatures. Dehydration can also cause problems during cold weather since water plays an important role in temperature regulation.

Some causes for these differences, however, can lie even deeper than subcutaneous fat, down in our DNA. Recent studies showed that genetics may play a bigger role than first known. A genetic variant resulting in changes in the alpha-actinin-3 (ACTN3) gene resulted in the absence of a muscle protein with the same name. This gene’s role used to be commonly known as the “gene for speed” in athletes, as these fibres allow the rapid contractions that facilitate sprinting. Researchers in Lithuania, Sweden, and Australia discovered a new role for this gene, in insulation.

A study conducted in Kaunas, Lithuania tested the relationship between cold perception and protein deficiency due to the ACTN3 genetic mutation. Men participants were plunged into cold water until their core body temperature reached 35.5 degrees Celsius. The researchers noted the time taken before the shivering set. Those lacking ACTN3 shivered less and had a higher core temperature compared to their protein-bearing counterparts. It is unclear whether this trend is similar in women’s bodies as more research still needs to be done. Regardless, the study’s findings imply a bigger role of genetics in temperature regulation than first assumed. 

This ACTN3 protein deficiency may be more common than you think, affecting one out of five people, and implies that some people are quite literally ‘built different.’ 

The interplay of genes and physiological responses is a particularly sensitive one; even the smallest changes can cause it to go haywire. 

The previously mentioned Raynaud’s disease is a condition that increases sensitivity of blood vessels to cold temperatures, resulting in spasms. These spasms in turn drastically reduce blood flow to fingers, toes, and joints causing soreness. In extreme cases, amputation may be necessary, but typically treatment is less drastic. Simple changes in lifestyle to avoid extreme cold are often sufficient to avoid loss of appendages. The causes of Raynaud’s disease are not entirely clear but highlight how even a small glitch in the complex system of temperature regulation can result in painful, even debilitating symptoms.  

Our choice of attire is dictated by our biological makeup. The conversations constantly happening in our body through neurotransmissions and hormonal messaging hinge on the library of information tucked away in the nucleus of each cell in our bodies.