7 Days Without Washing: Putting a Wool T-Shirt to the Test
When researching Merino wool, you will often see claims such as “Merino wool naturally resists odors” or “Because it does not retain odors easily, it does not need to be washed as often.”
It is reasonable to wonder, “Is that really true?” I usually wear UNIQLO AIRism as a base layer, but once I sweat, it develops a noticeable odor, so I always wash it after one day. Wearing it again the next day without washing would be unthinkable.
To put Merino wool’s natural odor resistance to the test, I wore a Merino wool T-shirt nearly 24 hours a day for about one week.
Results After Wearing a Merino Wool T-Shirt for One Week
For this test, I wore C-one’s “C FLEX Merino Wool T-Shirt” nearly 24 hours a day for one week.
Wear Test Details
Here are the conditions used for the wear test.
■ About the Wearer
- 28-year-old male
- Height: 163 cm; weight: 67.1 kg. The reference weight for this height is 58.5 kg.
- Walks about 10,000 steps a day, three to four days a week
- Does strength training at the gym about twice a week and has around 18 months of training experience
- Does not drink alcohol or smoke
- Rarely eats oily or spicy food
- Drinks protein shakes two or three times a day
- Tends to sweat heavily on the back and underarms; the back of the shirt can become soaked
■ Wear Conditions
- Wore the Merino wool T-shirt directly against the skin as a base layer
- Exercised while wearing the T-shirt
- Removed the T-shirt only to bathe
- After work each day, my wife checked the T-shirt for odor
- The test would end as soon as any sweat odor was detected
■ Detailed Test Conditions
- Test period: 12:00 a.m. on Monday, June 3, to 9:00 p.m. on Monday, June 10—nearly eight days
- Exercise: 10,000 steps every day except Sunday, June 9, plus a 90-minute gym workout on Thursday, June 6
※I went to the gym once and reached 10,000 steps on seven of the eight test days.
▼ Step counts recorded with Samsung Health
■ Weather and Temperatures During the Wear Test in Osaka
| 6/3 | 6/4 | 6/5 | 6/6 | 6/7 | 6/8 | 6/9 | 6/10 | |
|---|---|---|---|---|---|---|---|---|
| Weather | Sunny | Sunny | Sunny | Cloudy | Sunny | Cloudy | Cloudy, then rain | Cloudy, then sunny |
| High | 26.1℃ | 25.6℃ | 28.6℃ | 26.2℃ | 29.4℃ | 30.1℃ | 22.5℃ | 28.9℃ |
| Low | 16.2℃ | 16.3℃ | 16.9℃ | 17.6℃ | 19.3℃ | 19.0℃ | 18.7℃ | 17.8℃ |
| 10,000 steps | Yes | Yes | Yes | Yes | Yes | Yes | No | Yes |
| Gym | No | No | No | Yes | No | No | No | No |
Wear Test Result
At around 9:00 p.m. on Monday, June 10, I noticed sweat odor around the underarms and ended the wear test. My wife said, “It smells a little,” and we confirmed that the odor was coming from the underarm area. Because the odor may have begun while I was at work, I cannot say exactly when it started. Still, for someone who sweats heavily, the T-shirt remained free of noticeable odor for nearly a week.
The outcome may differ under the following conditions.
- If the test is conducted in a different season with the same level of exercise
- If the wearer’s gender, age, weight, or other physical conditions are different
- If the wearer drinks alcohol or smokes
- If the wearer often eats oily or spicy foods
- If the wearer does not exercise
- If the amount of exercise is greater
- If the wearer sweats more than the tester
The T-shirt Worn in This Test: C FLEX Merino Wool T-Shirt
Made in Japan with Super100’s Merino wool.
Lightweight, soft, washable at home, and ideal for everyday wear.
For Everyday Wear, It May Stay Fresh Even Longer
This wear test included a substantial amount of exercise, making the conditions fairly demanding. As loungewear, I felt the T-shirt might remain wearable for up to around two months without developing a noticeable odor. For ordinary outings with lower activity levels than this test, it might remain wearable for roughly two weeks to one month without washing.
Most people do not wear the same garment 24 hours a day, and clothing choices naturally change with mood and occasion. Some people may also wear another base layer under the Merino wool T-shirt, so individual results can vary significantly.
Next time, I would like to repeat the test under conditions closer to everyday life and see when odor begins to develop.
Product Used in This Wear Test
| Price | ¥16,500 (tax included) |
|---|---|
| Size | S / M / L / LL |
| Material | 100% Merino wool |
| Country of origin | Made in Japan |
Even after nearly a week of continuous wear by someone who sweats heavily, this T-shirt demonstrated impressive odor resistance. We invite you to experience that performance for yourself.
First-time customers can shop with confidence thanks to free domestic shipping and size exchanges within seven days for unworn items.
What Happens If You Do Not Wash a Merino Wool T-Shirt?
As this experiment showed, odor will eventually develop, so the T-shirt should be washed as needed. Unlike a conventional T-shirt, however, a Merino wool T-shirt does not need to be washed after every wear. You may wonder, “Then how often should I wash it?” As a general rule, wash it when it becomes visibly soiled or begins to smell.
If you simply prefer to wash it sooner, follow whatever schedule feels comfortable. For detailed instructions, see “Care Guide: How to Keep Loving Your C-one Merino Wool for Years to Come.”
Summary
What did you think of this wear test? Before starting, I expected it to last only about three days, so I was genuinely surprised that it continued for a full week.
At times I wanted to change into a different T-shirt, and wearing the same garment nearly 24 hours a day was mentally challenging. Still, the experience allowed me to feel Merino wool’s natural odor resistance firsthand, making the test worthwhile.
If you sweat often or are concerned about body odor, consider trying a Merino wool T-shirt and experiencing its natural odor resistance for yourself.
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