Sylaps

Applying undiluted lime juice or baking powder directly to the delicate skin of your underarms can easily cause chemical burns, severe irritation, and post-inflammatory hyperpigmentation, which will actually make the darkness worse.
​Baking powder is alkaline and disrupts your skin's acid mantle, while lime contains concentrated citric acid and psoralens that can trigger phytophotodermatitis and stinging. Baking soda is also an abrasive exfoliant that creates micro-tears in thin armpit skin.
​If you still want to use turmeric for its natural brightening and anti-inflammatory properties, a gentler, buffered formulation is much safer:
​Gentler Turmeric Mask
​1/2 teaspoon turmeric powder (brightens and calms inflammation)
​1 tablespoon plain, unflavored yogurt (contains lactic acid, a mild and hydrating alpha-hydroxy acid)
​1/2 teaspoon raw honey (acts as a soothing humectant)