Sorry, but me and seven people I know with chronic sinusitis have perfect
nails.

Must be something wrong with us, eh?

Medical Encyclopedia

Yellow nail syndrome

Yellow nail syndrome is characterized by yellow nails that lack a cuticle,
grow slowly, and are loose or detached (onycholysis). Yellow nail syndrome
is most commonly associated with lung disorders, and with lymphedema.
Update Date: 11/13/2006

Medical Encyclopedia

Yellow nails

Yellow nails are seen in the 'yellow nail syndrome' in which there is
thickening and yellow to yellow-green discoloration of all nails.
Lymphedema, especially of the ankles, and compromised respiration may be
present. The nails may also be over-curved both transversely and
longitudinally. Lunulae and cuticles may also be lost.
Update Date: 4/12/2007

Updated by: David A. Kaufman, M.D., Assistant Professor, Division of
Pulmonary, Critical Care & Sleep Medicine, Mount Sinai School of Medicine,
New York, NY. Review provided by VeriMed Healthcare Network.

Go to a Dermatologist to find out the cause.

Could be fungual or yellow nail syndrome etc..