Hi,
How are you? This may also be due to an infection such as fungal infection, eczema, psoriasis, inflammatory disease or underlying medical conditions such as hypothyroidism, or anemia. If it persists, have this evaluated further by your dermatologist for proper management. Your medical history and some blood tests will help rule out the differentials mentioned. Take care and best regards.
I don't know how old you are, but eyebrows tend to thin as you age, especially the ends above the nose. Do you have any other symptoms besides the eyebrows and the dry skin?