Hi, There are a few possible causes. The areas you have mentioned that is under-breast area and thighs are friction areas which may rub against each other while walking for example. It is also prone to become sweaty and this can cause fungal infection in those areas which is very itchy. It may just look red or have white patches or become darker than your normal skin due to the persistent scratching. I would recommend an antihistamine such as Allergex or Deselex as well as a topical anti fungal cream like Clotrimazole cream. The other options are fleas or scabies so it is best to he treated for these too. Hope this helps. Let me know if I can assist you further. Kind regards, Dr. Raboobee