How to Diagnose the Cause of Dry Nose in Cats
To diagnose the cause of your cat's dry nose, first determine if it has a fever. To carefully take its temperature, lube a digital thermometer with petroleum jelly, then hold your cat like a football while you gently insert the thermometer about 2 inches into its rectum. The normal range of temperatures for a cat is 100 to 100.2 degrees Fahrenheit. If it doesn't have a fever, test to see if the dry nose is from dehydration by pinching the skin just behind its neck and pulling up to create a tent. Next, release the skin and if it doesn't immediately go back down, your cat is dehydrated.
Look up the normal range of cat temperatures. A cat with a dry nose could have a fever. Before taking your cat to the vet, you can take its temperature at home. The normal range of temperatures for cat is 100–102.5 degrees Fahrenheit (37.8–39.2 degrees Celsius). Take your cat’s rectal temperature. A cat's temperature can be taken rectally or in the ear. Ear temperatures are not very accurate, so it is better to take a rectal temperature. If you do not already have a digital thermometer, purchase one at your local pharmacy, along with some lube (KY jelly, petroleum jelly) to put on the thermometer. To take your cat's temperature, place some lube on the thermometer. Hold your cat like a football, with its hind end facing you, and gently insert the thermometer about two inches into your cat's rectum. Remove the thermometer when it beeps and read the temperature. If your cat has a fever, you will need to take it to the vet. If your cat resists you taking its temperature, have your veterinarian take the temperature. Do not rely on the warmth of your cat’s nose. A dry nose can also be warm. However, a warm nose doesn't necessarily indicate a fever. Your cat's nose may be warm because your cat has been sitting or lying in a sunny spot. Also, because a cat's normal body temperature is higher than a human's body temperature, a cat's nose may naturally feel warm to the touch. Create a tent with your cat’s skin. A dry nose can also be caused by dehydration. One way to test for dehydration is to make a 'skin tent.' To make the tent, use your thumb and index finger to pinch and pull up a piece of skin from the scruff (just behind your cat's neck). Release the skin. If the skin stays in place, your cat is dehydrated. For a well-hydrated cat, the skin would immediately go back down. Check the color of your cat’s gums. If your cat has a dry nose, the gums can also indicate if dehydration is causing the dryness. In a healthy cat, the gums will be bright pink. In a dehydrated cat, the gums may be white. Measure the capillary refill time. If your cat has pink gums and a dry nose, you may wish to check their circulation. Gently press your index finger against your cat's gums for a few seconds, then lift your finger. Your cat's gums should become briefly pale, then quickly return to pink once the capillaries refill with blood. If the gums stay pale or take longer than two seconds to go back to pink, your cat could have circulatory problems. Visit a vet promptly for a diagnosis, since this may be a sign of a serious medical issue such as heart disease or anemia. Determine if your cat is drinking less. Monitoring your cat's water intake is another way to test for dehydration. If your cat is drinking less than usual, then it may be dehydrated. If you can, watch your cat to see if it is walking to its water bowl less frequently than usual. You could also measure how much water your cat is drinking. In the morning, use a liquid measuring cup to put an exact amount of water into your cat's water bowl. At the end of the day, pour the remaining water back into the measuring cup to determine how much (or how little) water your cat drank on a given day. If your cat is showing any signs of dehydration, take it to your vet. Look for cracks in the skin on the nose. A cat's nose can become so dry that it starts cracking. This can indicate a serious skin problem called pemphigus foliaceus. This condition can also cause the skin on the nose to look crusty. Pemphigus foliaceus requires veterinary treatment. Check the nose for sores and blisters. Pemphigus foliaceus can also cause the skin on a cat's nose to develop sores and blisters. These skin lesions can start to ooze, so you may also see discharge coming from the skin on your cat's nose. Take note of when your cat’s nose is dry. If your cat's nose is normally dry, there probably is not a problem. However, if your cat's nose is usually cold and wet, then suddenly becomes dry, your cat may have an underlying health problem. Decide if a visit to the vet is necessary. A dry nose in your cat may or may not indicate a health problem. If your cat looks otherwise healthy (eating, drinking, and grooming normally; still playful), a dry nose likely isn't something for you to worry about. However, if your cat has the signs listed below, along with a dry nose, you should take your cat to the vet: Fever Dehydration Tiredness Decreased appetite Crusty nose with sores and/or blisters Have your vet examine your cat. If you think your cat's dry nose is a problem, then a veterinary exam will be helpful to diagnose the cause. First, your vet will perform a physical exam of your cat. They will pay close attention to your cat's nose, then look for other signs of illness that you may have detected at home. If your vet thinks the dry nose is a problem, they may perform some diagnostic tests, such as blood work and skin samples, to determine the cause of the dry nose. Follow treatment instructions, if necessary. If your vet identified a health problem as the cause of your cat's dry nose, your vet will prescribe treatment for that problem. For example, if your cat has the skin disease pemphigus foliaceus, your vet will prescribe an anti-inflammatory medication (pemphigus foliaceus attacks the immune system). 
Look up the normal range of cat temperatures. Take your cat’s rectal temperature. Do not rely on the warmth of your cat’s nose. Create a tent with your cat’s skin. Check the color of your cat’s gums. Measure the capillary refill time. Determine if your cat is drinking less. Look for cracks in the skin on the nose. Check the nose for sores and blisters. Take note of when your cat’s nose is dry. Decide if a visit to the vet is necessary. Have your vet examine your cat. Follow treatment instructions, if necessary. 