As an expert in skincare, I can provide you with some insights on the topic. Aloe vera is often used for its soothing and hydrating properties, but its effectiveness in lightening underarms may vary from person to person. Aloe vera contains compounds like aloin, which may have a mild bleaching effect on the skin. However, the concentration of aloin in commercially available aloe vera products is typically low, so the lightening effect may be limited.

Additionally, the time it takes for aloe vera to lighten underarms can depend on various factors, including the individual's skin type, the severity of the pigmentation, and how consistently the aloe vera is used. It's important to note that results may not be immediate, and it may take several weeks or even months of regular application to see any noticeable lightening effects.

To use aloe vera for underarm lightening, you can apply pure aloe vera gel or products containing aloe vera to the underarm area daily. Leave it on for about 15-20 minutes, then rinse it off with lukewarm water. Remember to perform a patch test before applying any new product to ensure you don't have any adverse reactions.

However, if you're concerned about underarm pigmentation, it's always a good idea to consult a dermatologist. They can provide personalized advice and recommend suitable treatments or products based on your specific needs.