There are many causes of eyebrow
hair loss.It can be due to alopecia,autoimmune disorders,eczema
,fungal infections,hormone imbalances,lupus erythematosus,over plucking ,infections,psoriasis,seborrhea,scleroderma,thyroid problems or due to use of certain medicines or chemotherapy.
It is important to get all these conditions evaluated as treatment depends on the confirmation of diagnosis.I sincerely advise you to consult a dermatologist.
Hope it helps.