Pink skin and loss of hair

I noticed that my dog has slightly pink skin on her chest and that  her fur seems to be very thin here, so that I can clearly see her skin. It doesn't seem to be bothering her nor does it seem to be sore. She suffers with allergies and is currently on Apoquel. What could this be please?

Hello!  It could be part of the allergy, if the area has itched (licked or scratched) and the hair been pulled out.  Alternatively, some treatments for allergies eg steroids reduce the immune response and can lead to secondary proliferation of demodex which live on the skin on small numbers anyway.  This can lead to patchy hair loss.  The pressure of a collar on the site could be another possibility; ringworm possibly another.  If the area is in a fold, it may be more probe to friction (and also heat etc) than other areas.  Foreign bodies such as seeds may also be on the list.  Hormonal factors can also predispose to patchy hair loss. So there are various possibilities - and more - and tests or trial treatments may be needed in order to tell which is applicable in any one case.