dark armpits, help!

so the title probably helped u figure out what my problem is..i have dark arm pits and i have an event to go to in about 3 weeks where i really want to wear a sleeveless dress but i dont want my dark armpits to be a problem, and i dont wanna awkwardly keep my arms by my side the whole time. 
how can i lighten my arm pits quickly from home stuff? my skin is insanely sensitive so trying actual lightening products from a store may be dangerous for me :/