Dark underarms are usually found in those who shave the arm pits regularly, so if you have been shaving all along and have recently shifted to waxing, it may take some time for it to lighten. Waxing does not cause darkening unless you are allergic to any of the ingredients like lemon and try to identify if this is the cause. Other causes for dark underarms include excessive sweating, the use of strong deodorants: roll on or sprays, the build up of dead skin, inadequate cleaning of your underarms and an allergy to some sort of fabric: nylon or rayon. Tight blouses that cause friction or a reaction to chemicals and alcohol can also result in darkened underarms. Occasionally they are also the sign of some underlying disease and occur in those who are diabetic. It would be advisable to visit a doctor and get your blood sugar levels tested among other things.
On the home front, you can try rubbing slice of lemon onto your underarms as it acts as an excellent bleaching agent. If you have blisters in the region wait for it to heal before using lemon as it may cause a burning sensation. Coconut oil is a popular remedy for skin eczema and the vitamins and minerals it contains will nourish the skin. It acts as a natural moisturizer and will lighten the area in a few months. A paste made out of rose water and sandalwood powder can be applied onto the underarms and washed off in 20 minutes with cold water. You can also mix half a teaspoon of turmeric powder, the juice of half a lemon and a teaspoon of cucumber juice till it is in a paste form. Apply this on the darkened region and rinse thoroughly in 15-20 minutes. The antiseptic properties of turmeric will help clear out any infection and you should be able to see results in a month or so. Dry orange peels in the shade and grind it to make a semi-fine powder. Mix it into half a cup of unflavored yogurt and use as a scrub over your underarms. Apart from this you can try mixing milk, yogurt, and gram flour in equal proportions and add a pinch of turmeric powder to it. Apply onto the area and rinse off when completely dry. Potatoes thinly sliced and placed over the region can also help to a great extent.