Microbes that will cause respiratory or any other problem in the body will enter the system through our Respiratory tract only (Leaving apart injectables, or animal bite or sting etc.). We are inflicted by any disease, only when our immune system weakens. Thus, if our Respiratory System is strong, we can easily keep many problems at bay, including Sinusitis.
There can be innumerable reasons for your sore, running nose, or other respiratory related infection like, intake of toxins or Sinus, via modern day eating style, air/water pollution, various allergies, emotional downfall etc. Without going into any more theoretical details, and just keeping one thing in mind, that God has given us a very Technologically Advanced Body, which itself can take care of it, only if we eliminate the intake of toxins into our Divine Body.
Now, a brief about Sinusitis: There are air-filled spaces in the bones of our body. I, here am talking in respect of only Face and Forehead. The Inflammation in these spaces prevents the proper drainage of mucus, and this may also lead to infection. Symptoms include Nasal Congestion/Pressure, Pus Like Nasal Discharge (In case bacterial infection has developed), teeth pain, ear pain etc.
The dark spots that you see in the picture, have inflamed, mucous accumulated, not able to drain out.
So, we just increase the Pitta, and reduce Kapha, and increase The Nerve force a bit, and we should be OK!