Treatment
Undress immediately after your exposure to chigger habitat and take a warm, soapy shower. Pay special attention to scrubbing the areas around your ankles, waistline, underarms and anywhere there are folds or creases in your skin. Wipe the "chigger hot spots" (ankles, waistline) down with a bit of rubbing alcohol. Have someone examine you for chiggers. Remember that they're extremely tiny, but if you find one soon after being outside, you can remove it before it starts biting. Wash the clothes you wore outside before putting them on again.
Topical Cortisone creams can be very helpful to reduce the itching. Chigger mites frequently lay eggs underneath the skin, and Lindane (Kwell), which is also used for head lice, can be very effective, as well as asking your healthcare provider for Permethrin (Elimite). These medications usually take care of the chiggers fairly quickly.
The only ultimate cure is time, since there is nothing you can do to dislodge the chigger's feeding tube, the true cause of your itch. You must simply wait until your body breaks down and absorbs the foreign object.
In the meantime, local anesthetics such as benzocaine, camphor-phenol and ammonium hydroxide may provide you with several hours of comfort at a stretch. Over-the-counter creams can also help. In rare cases, some people are allergic to chigger bites and require prescription medications from their doctor.
The popular home remedy for which there is little justification is to dab nail polish on the welt. This cannot "smother" the chigger because it has not burrowed into your skin, and it was probably scratched off long ago. The only benefit to applying a thick coat of nail polish is that it helps to remind you not to scratch the bite.
Taken from: https://www.todayscacher.com/2005/may05/health.asp
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