。
I have chronic dermatitis.
Literal
Chronic's skin-inflammation [subject-が] exists.
Note how Japanese 'having' an illness is expressed with ある ('to exist'), not 持つ ('to hold'). The condition is marked with が as the grammatical subject of 'exists.' 慢性の uses plain の instead of 慢性的な — both grammatical, but の gives a more noun-like, formal effect. 皮膚炎 is a medical compound: 皮膚 (skin) + 炎 (inflammation).