A rash is a manifestation of dermatitis, and dermatitis can appear as a rash. So there is no difference between the two, they are not a matter of equivalence, so dermatitis can appear rash, but the appearance of rash, not necessarily dermatitis, can be other skin diseases, such as psoriasis can appear rash, foot gas can appear rash. So dermatitis can appear as a rash, but the appearance of a rash, not necessarily dermatitis. This explanation may be more reasonable to explain the relationship between them, but there is no need to put them both together and compare them.