Why is my dog's underbelly skin dark? Food change or hot weather?

Thanks for using Petco Pet Education Center, formerly Petcoach! This is possibly due to allergies. It really comes down to figuring out what is causing his allergies so that they can be treated or the specific allergen avoided. A secondary infection is likely and also needs to be addressed. There are many things that can cause allergies though in most cases they can be broken down into 3 big categories: flea, food and environmental allergies. Allergies are usually worked up in a stepwise fashion starting with flea allergies as this is the easiest and cheapest to take care of. If not on a flea preventative, then it would be a good idea to get started on one. If already on one then it would be a good idea to change to something else (there are many new products out in the market). If not improved in 1-3 months then it is time to move on and check for food allergies by switching to a novel diet (new protein and new carbohydrate). If that does not seem to be the issue then you are left out having to check for environmental allergies which require blood and/or skin tests. Allergies can be very frustrating to deal with at first but so rewarding at the end when we are able to treat them effectively!

The pictures look like it could just be normal pigment change. As puppies mature their pigmentation can as well. If the skin is raised, thicker, crusty, or itchy then I would be concerned. If you have any concerns then I would encourage you to have him evaluated by your veterinarian. If there is a concern then a biopsy could easily be done at the time of his neuter. Best of luck and thank you for using Pet Coach.

Darkening or changing skin color can be due to disease including allergy, flea infestation, bacterial skin disease or fungal disease. Change of skin (or even hair) color can also be completely normal especially in puppies and young dogs.

Skin darkening can occur due to natural aging, low level irritation from infection or allergies, a healed wound or changes in hormone levels from hypothyroidism. Your veterinarian may be able to determine the exact cause after a thorough physical exam. I hope this helps and please feel free to post any additional questions.

Sometimes it is normal change that will change back with no attention to it. Other times this can be a sign of an yeast infection or a low thyroid. Typically you do have other signs associated with these disease such as hair loss or itchy skin and lethargy. If none are nites then you can just monitor for any changes

Looking at the lesions and considering the history of this occuring in Summer, I suspect that this is a rash developing in response to allergic reaction to pollen in the grass during the summer months. Any lesion weakens the skin barrier and can lead to infection so sometimes they will get infected and scan over. Giving antihistamines can help some dogs, but rinsing him off after a walk will also help to reduce the pollen stuck to his skin.

This can be caused by various reasons such as fleas, mites ,fungal infection, bacterial infection and allergies. the first 4 needs to be ruled out before we start treating for allergies. in order to do that first de-flea Pistol with a high quality flea treatment such as advantage spot on, if it doesn't help - take him to the vet in order to check for/treat the other possibilities. If everything is ruled out, then an allergy treatment can be started. Usually an hypoallergenic food is a good way to start together with anti histamines. if it doesn't help - the best solution is a medication called Apoquel which treats allergies with great success and without side effects.