i'd go for universal indicator, bromothymol blue and methyl red
i mean, they have the degrees of acidity (specific color changes)
they have wider ranges of color changes which will lead to the strength of acid
you will know the degree of acidity of the cosmetics
in fact, bromothymol blue is used to detect the slightest level of acid or base in a substance
universal indicator has the pH charts; the range is big so that you can measure the level of acidity effectively
methyl red is sensitive too as the other two mentioned earlier
the other way that's not included in your choices is the pH meter
unlike litmus papers which just have 2 results; either red or blue
phenolphthalein only colorless, pale pink
you won't know the degree of acidity
hope that helps
