Yellow sweat stains do not occur in all people. Various factors cause them to form on your clothes, not just armpit sweat. The secretion of sebum, active ingredients from anti-perspirants and your sweat composition are the main factors, depending on the composition. In some people, these components form yellow deposits that settle in the textiles and become stronger with every wash.
laulas helps and protects your outerwear from these yellow stains, but cannot prevent them because the cause is not the shirt.
Although citric and acetic acid help against yellow stains, they should not be used on laulas because the acid damages the membrane fabric over time and shortens the life of your laulas.
Tip: Very often, a new deodorant is the cause of the sudden appearance of yellow stains and increased odour. Maybe changing your deodorant again will help.