This is due to friction rub of the skin causing chafing skin. Chafing is a common feature in obesity where the thighs rub with each other to cause redness
and soreness. The other possibility is of an allergic reaction
to the soaps, shower gel etc. Apply moisturizer and wear cotton undergarments. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen
are also helpful. If the symptoms persist then consult a dermatologist
For cracked heels, soak feet or hands in warm soapy water to soften cracks. Then rub with a pumice stone and apply some moisturizer. You can also wear socks after applying moisturizers for the cream to take effect.
Hope it helps you. Regards.