Crotch Itch is probably pin worms. Research; 'herbal epazote’ for the parasite and followed by fresh cloves for the eggs. Use only as directed. Follow the directions for epazote, It is potent. Mexican use a little when cooking beans for flatulence.
I take niacin (B-3) which does cause a red body flush with itching and burning sensation. The niacin is causing the veins to expand and cleans cholesterol, calcium, toxins from heart and veins. Very important for the heart. The flush is caused by toxins stored under the skin to ‘flushed' out. I stand it as long as I can and then shower. Do not wear the same clothes after shower. When the body and veins are cleaned out the flush does not happan. Very important B vitamin used by Dr. Hoffer to help cure Schizophrenia. Do the research.