I've noticed that it typically just affects my white undershirts and mainly on the front of the collar. Never underarm sweat stains. Occasionally light shirt collars and also around the hem on a pair of white shorts.
It has bugged me for so long as I am diligent with cleaning my neck area (exfoliating etc) but the dilemma goes on. I thought about what I do differently there and it dawned on me that for some time I have used a Nivea moisturiser on my face and neck that generally has a built in SPF sunscreen. So I googled sunscreen stains and there appears to be a bit of consensus that it can be a cause. It ties in with the shorts having applied sunscreen to my legs.
I figured that women are more likely to use moisturisers with, or in addition to, a sunscreen. This room also has active women who spend more time outdoors than their sedentary peers, increasing the odds of sunscreen. I also figure women often wear light coloured clothing and therefore may have encountered this.
Anyway I think that's sufficient information to draw out any responses. I just banished about 15 white shirts (with dirty collars) to the duster box and bought brand new ones which I''d like to keep clean for longer. More importantly I want to spare some of the new business shirts and a white, linen smart casual shirt from the same fate.
Over to the womens...