Hello, Yes, rashes are due to allergy to Cephalexin and rashes are a common presentation of allergic reaction. If after taking Claritin the symptoms have relieved to some extent then you need not to worry and even you can take Benadryl for further relief. But if the symptoms are worsening then you can consult an emergency room. For now you can take a dose of anti-allergics like Benadryl and do cool compresses over the rashes. Taking cool water bath can also be relieving. You can also apply calamine lotion or Caladryl lotion over the rashes to soothe the skin. You should drink plenty of water to wean off the effect of medicine faster. Also, make a note to avoid taking another dose of Cephalexin and in future always indicate your doctor that you are allergic to it. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Honey Arora