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Sinus issue can be highly environmental, but a Vitamin A deficient can contribute. If you would like, you can add a powder "A "additive to your Amazon's dry food by sprinkling a tiny bit on it. The best method in increasing the amount of green veggies your Amazon is getting.
Now to the environmental issues!
First, where in this huge World are you! If in the US, a state or region would be very helpful.
Late Winter and Spring time are common times when the toll of low Winter Humidity displays the effects, commonly with bad sinus infections. Just as common by mid to late Spring Amazons will use their nails to attempt to pull out the blockage, which in turns irritates the nostril and skin loss can occur.
Good Vet care with flushing the sinus and nostrils during the Winter and early Spring helps.
But, Assuring that your indoor Humidity level is 45 to 50% or a bit higher if possible is better.
If you have a forced air heating system, change your filters more often.
If you have a forced air heating system, add a whole home, humidification system.
- if not, upgrade your in room air filter(s) and add a room humidification system.
NOTE: If your Amazon is have this kind of problem, just consider what your home environment is doing for you and your family. Consider this a family health issue when you look at costs.