Answer:
"How does/Does only using one brand of makeup, milk makeup that is vegan affect how the skin will react to makeup that doesn’t have many toxic ingredients?"
I would make this more percise and easier to read. It's a little long and wordy.
I would say this instead: How does one brand of milk and vegan makeup affect the skin's reaction to other makeup that has no toxic ingredients?
This way you're describing and adding adjectives in different areas that make more sense.
