Why Do My Sweaters Pill Under The Arm And How To Stop It

Sweaters are a staple of cold-weather wardrobes—cozy, stylish, and versatile. But few things are more frustrating than noticing unsightly little balls of fiber forming under the arms of your favorite knit. These pills not only look unattractive but can make even high-quality garments appear worn out prematurely. The truth is, pilling under the arms isn’t a sign of poor quality alone; it’s a common issue rooted in friction, fabric composition, and daily wear patterns. Understanding the science behind this phenomenon—and knowing how to address it—is key to preserving your sweaters’ appearance and longevity.

The Science Behind Sweater Pilling Under the Arms

Pilling occurs when individual fibers break due to repeated abrasion and then tangle together into small knots or balls on the fabric surface. While pilling can happen anywhere on a sweater, the underarm area is especially vulnerable because it experiences constant mechanical stress from arm movement, contact with bags or seat belts, and friction against shirt sleeves or outer layers.

Fabrics made from shorter staple fibers—like cotton, wool, and some synthetic blends—are more prone to pilling because these fibers are more likely to pull loose from the yarn structure. Knit fabrics, which have a looser construction than woven materials, also expose more fiber ends, increasing the chance of surface fuzzing and eventual pilling.

The underarms are also subject to moisture from sweat, which can weaken certain fibers over time. Even minimal perspiration alters the pH balance of the fabric and softens fibers, making them more susceptible to breaking and tangling. Combine moisture with constant rubbing, and you’ve created the perfect storm for pilling.

“Pilling is not always a defect—it's often a natural result of wear. How quickly it happens depends on fiber type, garment construction, and lifestyle factors.” — Dr. Lena Peterson, Textile Scientist at the Fashion Materials Institute

Fabric Choices That Influence Pilling

Not all sweaters are equally vulnerable. The material plays a major role in how resistant a sweater is to underarm pilling. Here’s a breakdown of common sweater fabrics and their pilling tendencies:

Fabric Type	Pilling Risk	Why It Pills
Cotton	High	Short fibers break easily; absorbs moisture, weakening structure.
Wool (Merino, Lambswool)	Moderate	Natural crimp resists pilling, but friction still causes issues over time.
Acrylic & Polyester Blends	Very High	Synthetic fibers are strong but prone to surface abrasion and static buildup.
Alpaca	Low-Moderate	Longer fibers and smoother surface reduce pilling risk.
Cashmere	Moderate-High	Luxuriously soft but delicate; fine fibers break with friction.
Blends with Nylon or Spandex	Variable	Nylon adds strength; spandex increases elasticity but may increase rubbing.

Interestingly, higher thread count and tighter knits tend to resist pilling better because fibers are held more securely. Garments labeled as “anti-pilling” wool or treated acrylics often use specialized spinning techniques that lock fibers in place, reducing surface fuzz.

Tip: When shopping for sweaters, check labels for tightly knit weaves and fiber blends with reinforced durability, such as wool-nylon mixes.

How Daily Habits Accelerate Underarm Pilling

Your routine may be contributing to sweater damage without you realizing it. Everyday behaviors significantly influence how fast pilling develops:

• Wearing backpacks or crossbody bags: Constant strap friction rubs against the underarm area, accelerating fiber breakdown.
• Layering shirts with rough seams: A stiff dress shirt cuff or synthetic lining can create micro-abrasions every time you move your arm.
• Using antiperspirants with alcohol: These dry out natural fibers and leave residue that attracts dirt and increases abrasion.
• Improper washing techniques: Machine washing delicate knits, using hot water, or aggressive spin cycles weakens fibers and promotes pilling.
• Overwearing without rest: Like any fabric, knits need recovery time. Wearing the same sweater multiple days in a row prevents fibers from rebounding.

A real-world example illustrates this: Sarah, a teacher in Portland, noticed her favorite cream merino sweater developed severe underarm pilling within three months. After tracking her habits, she realized she wore it five days a week, carried a heavy tote bag daily, and machine-washed it occasionally when it smelled musty. Once she switched to hand-washing, rotated her sweaters, and used a breathable cotton liner beneath her arms, pilling slowed dramatically—even though she continued wearing the same style.

Step-by-Step Guide to Prevent and Reduce Underarm Pilling

Preventing pilling doesn’t require drastic changes—just consistent, mindful care. Follow this timeline-based approach to protect your sweaters:

1. Before First Wear (Day 1): Turn the sweater inside out and gently brush the underarm area with a soft clothes brush to smooth any loose fibers. Consider applying an anti-pilling fabric spray if available.
2. Daily Wear (Ongoing): Wear a thin, smooth undershirt made of silk, bamboo, or fine cotton to create a protective barrier between skin and sweater. Avoid bulky layers that increase friction.
3. After Each Wear (Within 24 Hours): Hang the sweater on a padded hanger and let it air out for several hours. Lightly pat the underarms with a dry towel to absorb residual moisture.
4. Every 3–5 Wears: Inspect the underarm area. If minor fuzz appears, remove pills with a fabric shaver or sweater stone—don’t wait until large bobbles form.
5. Deep Cleaning (Every 4–6 Weeks): Hand wash in cool water with a gentle wool detergent. Never wring or twist. Lay flat to dry away from direct heat or sunlight.
6. Storage (Seasonal): Fold sweaters and store them in breathable cotton bags. Avoid hanging, which stretches shoulders and distorts shape. Add cedar blocks to deter moths without harsh chemicals.

This routine minimizes stress on high-friction zones and keeps fibers strong. Prevention is far more effective than trying to reverse damage after pilling sets in.

Effective Tools and Techniques to Remove Existing Pills

If your sweater already has underarm pilling, don’t give up on it yet. Modern tools can restore its appearance with minimal effort:

• Fabric Shaver: A battery-powered device that trims pills cleanly. Use gently in one direction to avoid snagging.
• Sweater Stone or Pumice: A natural volcanic rock that lifts and breaks pills through light abrasion. Ideal for delicate cashmere.
• Razor Method: With caution, a clean disposable razor can be used on sturdy knits. Stretch the fabric taut and glide lightly—never press down.
• Lint Roller: Effective for removing loose pills but won’t fix embedded fuzz.

After de-pilling, always wash the sweater according to care instructions to remove loose fibers and reset the fabric surface. Note that removing pills improves appearance but doesn’t strengthen weakened areas—ongoing protection remains essential.

Tip: Test any de-pilling tool on an inconspicuous area first, like the back near the hem, to ensure it doesn’t damage the knit.

Checklist: How to Stop Sweater Pilling Under the Arms

Use this practical checklist to build long-term sweater care habits:

• ✅ Wear a smooth undershirt to reduce skin-to-sweater friction
• ✅ Rotate sweaters to allow fibers to recover between wears
• ✅ Avoid carrying heavy bags that rub against underarms
• ✅ Hand wash or use delicate cycle with cold water
• ✅ Always lay flat to dry—never hang wet knits
• ✅ De-pill early before bobbles become large and numerous
• ✅ Store folded in a cool, dry, ventilated space
• ✅ Use natural moth deterrents like cedar instead of plastic wraps

FAQ: Common Questions About Sweater Pilling

Is pilling a sign of low-quality clothing?

Not necessarily. Even high-end sweaters made from premium fibers can pill under the arms due to friction and wear. However, better construction—such as tighter knitting and blended reinforcement fibers—can delay the process significantly.

Can I completely prevent pilling?

You can't eliminate pilling entirely with regular wear, but you can drastically slow it down. Combining proper layering, careful washing, and preventative maintenance will keep your sweaters looking fresh much longer.

Does washing cause pilling?

Improper washing accelerates pilling. Agitation in machines, hot water, and harsh detergents weaken fibers. Always follow care labels: hand wash delicate knits, use mild soap, and avoid the dryer.

Conclusion: Protect Your Sweaters with Smarter Care

Underarm pilling is a common but manageable issue. It stems from a mix of physical forces—friction, moisture, and fiber vulnerability—not just poor craftsmanship. By choosing better fabrics, adjusting daily habits, and adopting a consistent care routine, you can preserve the look and feel of your sweaters for seasons to come.

Remember, a well-maintained sweater isn’t just about appearances; it’s a sustainable choice. Extending the life of your clothing reduces waste and saves money over time. Small actions—like wearing an undershirt, folding instead of hanging, or using a fabric shaver early—add up to big results.

💬 What’s your go-to method for keeping sweaters looking new? Share your favorite tip or ask a question in the comments—let’s build a smarter wardrobe together!