Why You Feel Sluggish on May Afternoons: Sweat Chill and the T-Shirt That Helps Protect Your Autonomic Nervous System
Once May arrives, more days begin to feel like summer, with daytime temperatures approaching 30°C. After sweating during your commute or while moving around outside, many people have experienced stepping into an air-conditioned office or train and suddenly feeling chilled to the core.
That sudden “shiver” is not just a minor discomfort. It is a sign that your autonomic nervous system is working hard to cope with a rapid temperature change and has begun consuming energy. When you feel sluggish in the afternoon for no obvious reason, one hidden cause may be the “sweat chill” you experienced earlier that morning.
In this article, we look at the relationship between sweat chill and the autonomic nervous system from a scientific perspective, and explore why your choice of fabric can directly affect your afternoon performance.
THE SCIENCE The Evaporative Cooling Trap Cotton Shirts Cannot Prevent
When a liquid changes into a gas, it draws heat from its surroundings. This is known as evaporative cooling. In the case of water, the evaporation of just 1 gram removes approximately 580 calories of heat. The “cool” feeling you get when wind hits your skin after sweating is caused by this process taking place on the surface of your skin.
The problem is that ordinary cotton shirts can remain wet for 30 to 60 minutes. Until the fabric dries, evaporative cooling continues to pull heat away from the body. In an air-conditioned room, this effect becomes even stronger, causing the skin surface temperature to drop sharply.
AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system consists of two branches: the sympathetic and parasympathetic nervous systems. It automatically regulates body temperature, heart rate, digestion, and more. When the skin surface temperature drops suddenly, the sympathetic nervous system sends a command to “warm the body,” triggering blood vessel constriction, muscle tension, and increased metabolism all at once. This emergency response consumes a large amount of energy, which can later appear in the afternoon as fatigue and reduced concentration, almost like running out of fuel. The sluggishness you feel on days with large temperature swings is often caused by this autonomic fatigue.
In other words, the fundamental solution to sweat chill is not simply “toughing it out” or repeatedly putting on and taking off a jacket. It is choosing a fabric that prevents sudden changes in skin surface temperature in the first place.
Figure 1: Comparison of how sweat chill leads to autonomic nervous system stress. The issue is not “sweating” itself, but how the fabric behaves afterward.
THE DATA The Difference in Skin Surface Temperature, Shown in Numbers
After entering an air-conditioned environment, how does skin surface temperature change when wearing cotton compared with merino wool? The schematic image below shows the general pattern. With cotton, skin surface temperature drops sharply over the first 10 to 20 minutes after entering the room, then gradually recovers. The depth and duration of this “temperature dip” determine the level of stress placed on the autonomic nervous system.
Figure 2: Changes in skin surface temperature after entering an air-conditioned environment (schematic image; individual differences may apply). With cotton, the temperature may drop by up to approximately 1.9°C after 20 to 30 minutes.
MERINO WOOL SCIENCE
The reason merino wool releases moisture gradually lies in the internal structure of the fiber. The cortex inside wool fibers is hydrophilic and actively absorbs moisture, while the scale layer on the surface is hydrophobic. Thanks to this asymmetrical structure, sweat is taken into the fiber as vapor and slowly diffuses outward. This mechanism is fundamentally different from cotton, where liquid sweat evaporates all at once. Structurally, merino wool helps prevent the sudden drop in body temperature caused by evaporative cooling.
THREE FUNCTIONS Three Automatic Controls That Help Protect the Autonomic Nervous System
C-one’s merino wool (Super 100’s, 18.5μm) helps automate temperature regulation simply by being worn. These three functions work together to minimize stress on the autonomic nervous system throughout the day.
Sweat Chill Blocking — Neutralizing Evaporative Cooling
By absorbing moisture at the vapor stage and releasing it gradually, merino wool suppresses sudden evaporation on the skin surface. It structurally helps prevent the “shiver” you feel when entering an air-conditioned space, reducing the likelihood of triggering the autonomic nervous system’s emergency response.
Automatic Temperature Regulation — Cool When It’s Hot, Warm When It’s Cold
Wool fibers generate “heat of sorption” when absorbing moisture and provide a slight cooling effect when releasing it. This two-way function helps keep the wearer’s perceived temperature close to a comfortable range. As a result, the need for manual adjustments—such as repeatedly putting on or taking off a jacket—naturally decreases.
All-Day Dry Skin Environment — Blocking Stuffiness and Discomfort
By keeping the inside of the fibers dry, merino wool also helps suppress bacterial growth. Reducing concerns about odor removes a small but real source of mental stress in business settings. Body temperature is not the only factor that disrupts the autonomic nervous system—the accumulation of unpleasant sensations can also erode afternoon performance.
PRODUCT LINEUP Three Models Designed to Help Prevent Sweat Chill
Merino wool T-shirts that help minimize stress on the autonomic nervous system. Here are three models you can choose from according to your lifestyle.
C BASIC Merino Wool Short Sleeve T-shirt
A basic model with excellent core performance. Ideal as your everyday uniform. With a wide range of colors, you can choose the one that suits your style.
C HIGH END Merino Wool Long Sleeve T-shirt
A premium model suitable for business settings. Whether worn under a jacket or on its own, it creates a refined impression appropriate for the occasion.
C FLEX Merino Wool Short Sleeve T-shirt
A model designed for ease of arm movement. Perfect for active businesspeople and anyone who moves frequently throughout the day.
FAQ Frequently Asked Questions
Q: Does it really help prevent sweat chill in summer?
A: Merino wool, especially Super 100’s, absorbs sweat while it is still in the vapor stage and releases moisture gradually. This helps prevent the sudden evaporative cooling often caused by cotton shirts. However, results may vary depending on the individual and environment. For more details, please see our Care Guide.
Q: Which model should I choose?
A: C BASIC is ideal as an everyday uniform with essential performance. C HIGH END offers a refined feel suitable for business settings. C FLEX is best for those who prioritize ease of movement. Choose according to your purpose and lifestyle.
Q: How should I choose a color?
A: In terms of preventing sweat chill, there is no functional difference between colors. You can choose freely according to the impression you want to create in business settings or your personal preference.
Q: How should I wash it?
A: Place it in a laundry net and wash it as usual. No ironing is needed. For more details, please see our Care Guide.
Q: Are returns or exchanges possible?
A: Size exchanges are accepted within 7 days of purchase. Returns are also accepted within 30 days. For more details, please see our Shopping Guide.
TRUST & QUALITY Shop with Confidence
✓ Made in Japan, crafted by skilled artisans
High-quality Super 100’s merino wool is carefully tailored by skilled Japanese artisans.
✓ 7-day size exchange
If the size does not fit, we accept exchanges within 7 days.
✓ 30-day return guarantee
If you are not satisfied, returns are accepted within 30 days.
✓ Free shipping in Japan / Pay Later available
Free shipping on all domestic orders. Convenience store payment and Paidy are available, so you can shop with confidence.
An Investment in Eliminating Sweat-Chill Stress.
C-one uses Super 100’s merino wool while offering a wide range of colors rarely found elsewhere. Thanks to its natural temperature- and moisture-regulating functions, you can wear your favorite color in business settings without worrying about sweat chill or discomfort.
Find the one piece that helps support your afternoon performance.