Although skin temperature is less frequently discussed, it plays an important part in indicating sickness or recovery from an injury. It also gives us valuable information about our blood pressure, heart rate, sleep, exercise and overall metabolism.
A Primer on Skin Temperature
Our skin is the largest organ in our body and plays an important role in regulating our body temperature, a process called thermoregulation, a mechanism that allows our body to maintain its internal/core temperature despite the changes in the external environment. All thermoregulation mechanisms are designed to return your body to homeostasis or a state of equilibrium.
The skin on our bodies makes up roughly 15% of our total body weight, with the temperature of our skin varying throughout our bodies.
For example, the skin on the trunk of our body typically ranges from 33.5–36.9°C (92.3–98.4°F), and on the curved parts of our body (toes, fingers, nose and ears), the skin is typically cooler. Furthermore, superficial veins are usually lower in temperature as compared to superficial arteries.
The temperature of our skin can change depending on the temperature of the air, the type of environment we are in, circulation and physical activity. Our skin helps to maintain the internal homeostasis of our body in several different ways.
For example, when our core temperature starts to rise, the blood vessels on our skin dilate and release sweat, which evaporates into the air and helps to cool us down. Conversely, when our core temperature starts to decrease, the muscles on our skin called the arrectores pilorum start to contract, generating heat to help keep us warm.
When the hypothalamus, the part of our brain that controls thermoregulation, senses internal temperatures becoming too hot or cold, it will automatically send signals to the skin, glands, muscles and organs.
For example, when our body temperature rises during high-intensity exercise or if the external ambient temperature is elevated enough to cause a rise in the core temperature, afferent signals (messages from sensory nerves to the central nervous system) to the hypothalamus result in efferent signals (messages from the central nervous system to organs and limbs) to the cells of the skin to produce sweat.
Thermoregulatory responses can be either behavioural or autonomic. Examples of behavioural responses are changes in posture or location with regard to the environment. Autonomic responses are internal processes that lead to vasodilation (the widening of blood vessels), thermogenesis, and so on (like sweating, shivering, etc.).
Our skin is made up of three layers—the epidermis, dermis and hypodermis—and its three primary roles are to protect, regulate and sense.
Skin temperature is important to take into consideration when assessing our health because it can indicate when a person is sick or recovering from an injury. It also gives us valuable information about our blood pressure, heart rate, sleep, exercise and overall metabolism.
The temperature of our skin can be measured by using an infrared thermometer or a thermistor. Both devices are useful. However, infrared thermometers tend to offer faster readings and are more easily manoeuvrable, while thermistors are more responsive and provide more sensitive readings.
So what’s the difference between skin and body temperature?
The average temperature of our body ranges between 36.1–37.2°C (97–99°F), making it warmer than our skin temperature, which ranges from 33.5–36.9°C (92.3–98.4°F).
Factors that influence and are influenced by skin temperature
Let’s consider the factors that influence and are influenced by skin temperature. It can be a source of insights into our sleep quality, heart health, fitness levels and metabolic rate.
1. Skin Temperature and Sleep
Before falling asleep at night, our core temperature slightly drops which helps to stimulate drowsiness. This temperature drop is generally a fraction of a degree or slightly more. It typically occurs throughout the late afternoon and evening hours, leading up to bedtime, and remains in place throughout sleep.
When these internal temperatures begin to decline, we are likely to engage in calming rituals that lead us towards sleep, such as getting a warm blanket, lying down or slowing down our breathing. When we dissociate from this pattern, we generally experience a harder time falling asleep.
While our core body temperature drops in the evening, the temperature of our peripheral skin elevates to help us release heat from our body’s core. When our body temperature is low at night, our skin temperature is high, and conversely, when our body temperature is high during the day, our skin temperature is cool.
In the early hours of the morning, our core body temperature starts to rise and our skin temperature lowers. This helps to make us feel more awake and alert for the day ahead of us. If the connection between a slightly higher-but-still-normal body temperature and alertness seems counter-intuitive, consider how energized you feel immediately after exercising. Although there are other factors involved, one reason for this is that your temperature is slightly elevated.
These natural-body-temperature fluctuations of cooling before sleep and warming up before waking are intimately linked to our body’s circadian rhythms. When functioning properly, these rhythms follow an approximately 24-hour cycle that helps us sustain a regular sleep-wake schedule.
In one study conducted in the Netherlands, researcher Rolf Fronczek discovered that people with narcolepsy were able to stay awake more easily when their skin temperature was lowered, and their ability to fall asleep was influenced by warming up or cooling down their hands and feet.
After we fall asleep, our bodies do not respond as much to external temperature fluctuations. In fact, during rapid eye movement (REM) sleep, our bodies nearly stop regulating temperature altogether. This limits normal temperature-regulating mechanisms, such as sweating or shivering, and means we’re more susceptible to being adversely affected by external temperatures when we’re asleep than we are when awake. For instance, we’re likely to heat up or feel cold much more quickly when we’re in the stage of REM sleep than during our waking hours.
2. Skin Temperature and Heart Health
Although it’s true that high blood pressure can be caused by poor dietary choices and a sedentary lifestyle, research has shown that our skin’s response to low oxygen may also affect the health of our cardiovascular system.
Researchers studied mice that lacked hypoxia-inducible factor (HIF, proteins that play a vital role in the body’s reaction to low oxygen concentrations or hypoxia) in their skin and then exposed them to low levels of oxygen. Compared to healthy mice in the same conditions, they found that the mice who lacked HIF-1-alpha and HIF-2-alpha experienced a decrease in their physical activity and an increase in their heart rate, blood pressure and skin temperature.
Professor Johnson, who led this study, noted that because the skin is our largest organ, it makes sense that it plays an important part in blood pressure regulation.
In another study, 56 males participated in two walking trials, in controlled temperatures, while researchers monitored their core and skin temperatures, heart rate and physical strain index (which evaluates heat stress). They discovered that the heart rate and skin temperature, in relation to the physical strain index, were extremely accurate in assessing heat risk status.
3. Skin Temperature and Exercise
Skin temperature plays a vital role in thermoregulation when we exercise. During exercise, our skin helps to regulate the internal temperature of our body by providing negative or positive feedback to our thermoregulatory system. Studies show that aerobic fitness is positively associated with an increased skin temperature during exercise in male runners.
Interestingly, skin temperature can be affected by both high-intensity and low-intensity exercise. During high-intensity exercise, there is an increase in blood flow to the skin. The increased blood flow is due to the body’s need to dissipate heat generated by the muscles. The flow of blood causes the skin temperature to rise.
In contrast, during low-intensity exercise, there is less demand for dissipating heat, and blood flow to the skin is reduced, leading to a decrease in skin temperature.
Our skin temperature is also influenced by our fitness level, which, along with our age, plays an important role in dictating how much cutaneous vasodilation (heat transfer from the body core to the skin) occurs while we exercise. Being inactive lowers our aerobic fitness, which lowers our heat-dissipation capacity and, ultimately, our ability to control our body temperature when we exercise. Research shows that a medium-to-high level of fitness can help us more easily regulate our internal body temperature, especially around our torso.
4. Skin Temperature and Metabolic Rate
Metabolism refers to a series of chemical processes in each cell that transform the calories we eat into fuel to keep us alive. These processes sustain life and everyday functioning and include breaking down food and drink for energy and building or repairing our bodies.
Research shows that higher core body temperatures appear to increase metabolism. A review published in 2009 in Transactions of the American Clinical and Climatological Association reports that an increase in body temperature is associated with a higher metabolic rate, and higher body temperatures do speed up metabolism. Thus, body temperature is a fairly reliable guide to metabolic rate.
When people lose weight, their body temperature drops as their metabolism slows down. This is why some people feel cold all the time when they’re dieting, especially if it’s a crash diet. Various studies have shown that there is a connection between the number of calories consumed and the body temperature, which is directly tied to metabolism. Keeping track of your body temperature can help you determine what kind of metabolic response your body is having to a particular diet or workout routine.
The temperature of our skin also affects our metabolic rate. Research shows that exposure to cold temperatures can help increase energy expenditure without increasing appetite and energy intake.
In a research study, participants were exposed to mildly cold temperatures and it was seen that during the first 30 minutes, the temperature of their skin dropped and then remained stable.
The temperature of the sternal area compared to the subclavicular area was lower. Interestingly, there was a positive correlation between the temperature of the skin in the sternal area and an increase in energy expenditure.
Research suggests that insulin-induced hypoglycemia lowers rectal and tympanic (ear) temperatures by 0–2°C (3.60°F).
Conclusion
Skin temperature can give us valuable information about our blood pressure, heart rate, sleep, exercise and overall metabolism.
On account of the fact that it is constantly exposed to the environment around us, the temperature of our skin changes more frequently than our core temperature and is able to survive temperatures that could be damaging to our internal organs. When our body temperature is low at night, our skin temperature is high, and when our body temperature is high during the day, our skin temperature is cool.
Although it’s true that high blood pressure can be caused by poor dietary choices and a sedentary lifestyle, research has shown that our skin’s response to low oxygen may also affect the health of our cardiovascular system.
Our skin temperature is also influenced by our fitness level. Research shows that higher core body temperatures appear to increase metabolism and that exposure to cold temperatures can help increase energy expenditure without increasing appetite and energy intake. Although skin temperature is less frequently discussed, it plays an important part in our overall health.
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns before undertaking a new healthcare regimen including making any dietary or lifestyle changes.
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