The purpose of this study is to assess whether tralokinumab can be a helpful treatment for alopecia areata. This is a randomized, double-blind, placebo-controlled pilot study of a total of 30 subjects with moderate to severe alopecia areata involving 30-100% of the scalp. Expected is 50% of these subjects to have concomitant alopecia areata (AA) and atopic dermatitis (AD). Subjects with AA alone (15 subjects) will be randomized (2:1) to either receive tralokinumab or placebo via subcutaneous injection every 2 weeks for 24 weeks. Subjects with concomitant alopecia areata and atopic dermatitis (15 subjects) will be randomized separately in a 2:1 ratio to receive tralokinumab or placebo via subcutaneous injection every 2 weeks for 24 weeks.