My daughter, 38yrs old has skin eczema on her feet. they are cracked pretty bad. this morning there is a knot or boil on her heel that is very sore.

Infected eczema: It sounds like your daugher has infected eczema. She should be evaluated for a strep or staph infection once infection is treated the eczema should be aggressively treated by a dermatologist.

Secondary infection: She probably has a secondary infection from the opening that occurred from the fissures. If she is diabetic this can be dangerous and she needs to see a doctor for debridement of the lesion . If she isn't diabetic she can try otc antibiotic cream , if it doesn't get better she needs to see a doctor for PO antibiotics. Ultimately her goal should be to treat the eczema to avoid future infections, .