To grade underarm staining on used shirts, run a lift-and-light test: lift the underarm fabric away from the body, check it under angled light, and see whether the yellowing sits on the surface or has changed the fiber. Surface residue that washes out is a cleaning task. Yellowing that stays after a proper wash is a grade-lowering defect, usually Good or Fair depending on spread and stiffness.
Here is the scenario we see weekly. A white Oxford looks clean flat on the table. The seller calls it Excellent. The buyer opens the box, holds the pit up to a window, and sees a faint tan crescent on both sides. Return opened, reason: not as described. The shirt was not filthy. The seller just never looked at the one spot buyers always check.
Why underarm staining needs its own test
Underarm marks are not one defect. They are at least three, and each one grades differently:
- Deodorant residue: white or gray buildup, often stiff or crusty, sitting on top of the fabric.
- Sweat yellowing: a yellow or tan tint caused by sweat reacting with antiperspirant ingredients and body oils, bound into the fiber.
- Fiber damage: thinned, stiff, or brittle fabric where salts and acids have worked on cotton over years.
The first is cosmetic and often removable. The second can be cosmetic or permanent. The third is a Fabric Condition problem, and no wash fixes it. If you treat all three as one stain, you will either underprice a shirt that was fine or overprice one that will draw a return.
The lift-and-light test, step by step
Do this before you wash, then repeat after. The point is to compare, so you know what the cleaning actually changed.
- Turn the shirt inside out and lay the underarm area flat. Note any crust, white film, or stiffness by touch before anything else.
- Lift the underarm fabric away from the table and hold it between you and a window or a daylight lamp. Transmitted light shows yellowing and thinning that flat photos hide.
- Switch to raking light: hold a lamp low and to the side. Residue shows as a raised, matte film. Set-in yellowing looks flat and tonal.
- Scratch gently with a fingernail. Residue flakes or lifts. Fiber-bound yellowing does not move.
- Pinch and flex the fabric. Stiff, papery, or crunchy cotton signals fiber change. Soft and flexible fabric is a better sign.
- Smell the area closely, then wash per the care label and let the shirt dry fully. Repeat steps 2 and 3 and record what remains.
Whatever is left after a proper wash is what you grade. Do not grade the shirt on the hope that a buyer will wash it better than you did.
Reading the results: cosmetic or grade-lowering?
The test gives you a pattern. Here is how we map it to condition factors and tiers.
| What you see after washing | Likely cause | Factor affected | Typical tier ceiling |
|---|---|---|---|
| No visible mark, soft hand, no smell | Residue fully removed | None | Unchanged (Excellent or better if the rest holds) |
| Faint tint visible only in transmitted light | Early sweat yellowing | Cosmetic Appearance | Very Good |
| Clear yellow or tan crescent visible flat | Set-in sweat stain | Cosmetic Appearance | Good |
| Yellowing plus stiffness or thin spots | Fiber damage | Fabric Condition | Fair |
| Holes, fraying, or fabric that tears when flexed | Advanced fiber breakdown | Fabric Condition, Structural Integrity | Poor |
Treat the tier column as a ceiling, not a verdict. A shirt with a faint pit tint and a missing button is capped by the button as well. The five factors are weighted together, and underarm condition feeds mainly into Cosmetic Appearance, Fabric Condition, and Odor & Cleanliness.
Cotton, blends, and vintage: where the rules shift
Fiber changes how the stain behaves.
100% cotton yellows readily because the fiber absorbs sweat and aluminum-based antiperspirant residue. It also tends to respond to enzyme soaks and oxygen-based cleaners, so a wash-then-retest is worth the time. Old, set-in yellowing on white cotton is often permanent.
Poly-cotton blends hold oils. The yellowing may be less visible, but the smell can linger in the synthetic fibers even after washing. Check Odor & Cleanliness separately and warm the underarm in your hands before sniffing.
Vintage shirts need extra care. A yellow underarm vintage shirt assessment has to ask whether the yellow is a stain or the fabric's age. Compare the underarm to the inside of the hem or a protected seam allowance. If the whole shirt has aged evenly, the pit is not a separate defect. If only the pit is darker and stiff, it is damage. Be cautious with aggressive cleaners on old fabric: you can turn a cosmetic mark into a Fabric Condition defect in one soak.
What to write in the listing
A grade only works if the note matches it. Keep the wording plain and specific, and photograph the pit in daylight with the fabric lifted.
- Clean after wash: "Underarms checked in daylight, no staining or residue after washing."
- Faint tint: "Light yellow tint under both arms, visible in bright light only. See photo 6."
- Set-in stain: "Yellow underarm staining on both sides, did not lift with washing. Fabric is soft and intact."
- Fiber change: "Underarm fabric is stiff and slightly thin with yellowing. Priced as Fair."
Add one close-up per side. On eBay, a not-as-described case often turns on whether the defect was visible in your photos or mentioned in the description. A pit shot with your note removes most of the argument. On Poshmark, the same photo cuts the offer that starts with "does this have underarm stains?"
Common mistakes that cost you money
- Grading on the flat photo. Transmitted light finds what a tabletop shot misses.
- Skipping the post-wash check. You do not know what is cleanable until you clean it.
- Bleaching a white shirt as a fix. Chlorine can intensify yellowing on some fabrics and weaken cotton. Use it carefully, or not at all.
- Calling stiffness "just starch." If it persists after washing, it is Fabric Condition.
- Pricing as Excellent and noting the stain in fine print. The grade and the price should agree.
Grade one shirt and compare
Pick the shirt in your pile with the most suspicious underarms, run the lift-and-light test before and after a wash, and write down what you find. Then grade the same garment in GradeThread and compare the report to your own call. You will see how Cosmetic Appearance, Fabric Condition, and Odor & Cleanliness each moved the grade, and you get a certificate a buyer can verify.