Nasal dermatoses are diseases of the skin on or near the nose. The nose itself is often referred to as the nasal planum. Some of these conditions are sometimes known as Collie nose or nasal solar dermatitis, depending on the cause.
Many diseases may cause these conditions in dogs. These may affect the bridge of the nose (the muzzle), the nose itself, or both. In cases of pyoderma (skin infection), dermatophytosis ("ringworm"), and demodicosis (a type of mite infestation), the haired portions of the nose are affected. In systemic lupus erythematosus or pemphigus (types of immune-mediated diseases), the whole muzzle is often crusted (with occasional oozing of serum) or covered with ulcers. In systemic and discoid lupus, and occasionally in pemphigus and skin lymphoma, the nose loses color and reddens; eventually the area near the nose may develop ulcers.
Nasal dermatosis due to solar radiation is probably a rare disease and may be misdiagnosed as lupus. In true nasal solar dermatitis, the nonpigmented areas around the nostrils are affected first, and occasionally the bridge of the nose may become inflamed or ulcerated. These changes are worse in the summer, although lupus and pemphigus may also show this seasonal variation.
Any of the above diseases may affect the areas around the eyes. The sudden onset of nasal swelling, redness, and fluid discharge is thought to be caused by an insect sting or bite. The parasitic disease leishmaniasis may cause color loss or ulceration on the nose.
Treatment depends on the cause. Diagnostic tests performed by your veterinarian will likely include skin scrapings, bacterial and fungal cultures, and biopsies. The prescribed treatment will depend on the results of the diagnostic tests.
If the diagnosis is nasal solar dermatitis, a topical steroid lotion may help relieve inflammation. Exposure to sunlight must be severely curtailed. Topical sunscreens may be effective but need to be applied at least twice daily. You should be aware that not all sunscreen lotions prepared for human use are safe for use on dogs. Your veterinarian can recommend a sunscreen that will be tolerated by your dog.