White deodorant stains under the arms on dark clothing are caused by the acidity present in antiperspirants, not sweat. Prevention can be less time consuming than removing the stains. There are antiperspirants on the market that are advertised as not producing white stains on dark clothing. They may be worth a try if these stains occur frequently or are difficult to remove. Gels and roll-on antiperspirants have more water in their formulas, which permeates clothing easily and leads to more staining than stick antiperspirants.
For dry-clean-only garments, take them to a professional dry cleaners and point out the white underarm stains. Dry cleaners have treatments for the problem. For washable fabrics, rinse the white stains with cold water. Then launder the garment using the warmest water recommended on the care label with normal detergent. Inspect the underarm area to see if the stain is gone before placing the garment in the dryer.
If the cold water treatment did not work, try a three-step process on the stain. Use cool water to dampen the area that is stained. Mix a mild detergent with cool water and add a few drops of ammonia. Press stain with an absorbent pad moistened with the solution every five minutes several times. Rinse with cool water.
Use cool water to dampen the area that is stained. Mix a mild detergent with cool water and add a few drops of white vinegar. Press stain with absorbent pad moistened with the solution every five minutes several times. Rinse with cool water.
With an absorbent pad, apply rubbing alcohol. Let stand on delicate fabrics as long as the stain is being removed. On stronger fabrics, tamp occasionally with a brush. Flush with water.
After applying the three-step process, launder as specified for the fabric involved but do not put the clothing in the dryer. Let air-dry naturally. Inspect the clothing to see if the stain is removed. If it is still there, the steps may need to be repeated. Once the stain is removed, the clothing may be dried in the dryer.
Use plain ammonia without any colour or fragrance.
Do not rub delicate articles of clothing or damage may result.