Those yellow pit stains are chemistry and it's reversible.

Chlorine bleach (sodium hypochlorite) reacts with protein-based stains through oxidation. On dye-based stains (wine, grass), this oxidation removes the color. On protein-based stains (sweat, blood), it INTENSIFIES the yellow by further oxidizing the protein compounds. The result: a darker, more set stain than before. The plan uses OXYGEN bleach (hydrogen peroxide), which lifts the yellow oxidation without the protein-darkening reaction.

Probably not. Even ancient stains respond to the enzyme soak (Method B) because enzymes dissolve protein bonds regardless of how many wash cycles have passed. The key: the protein layer is ON the fabric, not inside it (unlike bleach damage, which destroys fibers). Multiple enzyme soaks (2–3 rounds of overnight treatment) can dissolve years of buildup. The stain may not come out in one round, but each round removes a layer.

At 3% concentration (the standard drugstore kind), hydrogen peroxide is safe on MOST colored fabrics. However: some dyes are sensitive, especially dark reds, blues, and blacks. Always test on an inconspicuous area first (inside seam, hem) by applying a drop, waiting 10 minutes, and checking for color change. For colored fabrics where you're unsure: the enzyme soak (Method B) is safer because it relies on enzymes, not bleaching chemistry.

Yes, but NOT with the standard enzyme method. Silk and wool are protein-based fibers — protease enzymes can't distinguish between sweat protein and fabric protein, so they may damage these fabrics. The plan includes Method D (the aspirin soak: salicylic acid + cream of tartar) which is safe on delicates. For very valuable garments: a professional dry cleaner with stain-removal expertise is the safest option.

The yellow color is specifically caused by the reaction between ALUMINUM in antiperspirant and sweat proteins. Switch to an aluminum-free deodorant and the yellow staining stops entirely (you may still get salt stains from sweat, but these wash out easily with regular detergent). If you need antiperspirant: apply at night, let it dry, and wear an undershirt as a barrier between your skin and your dress shirt.