Additionally, smells and odor can be emanating from the anal glands. If they become compacted and then burst open, the smell can be quite overwhelming. An issue such as this should be checked by the vet, since skin tears can become infected.
If you suspect that the anal glands need expressing and you generally don't do this yourself, definitely make an appointment with the vet or a dog groomer.
Another element to look at is the condition and health of a Boxer dog's skin. Yeast infections or any type of skin infection can cause a nasty smell. Yeast dermatitis can develop on a Boxer dog of any age and at any time, however it will develop more easily if the dog is exposed to hot, humid weather.
Medical conditions and diseases that can cause skin yeast infections with bad odors are hypothyroidism, Cushing's Disease and allergies. Prolonged use of antibiotics and steroid based medication can cause this as well.
Oder, along with any signs of a rash, redness, swelling, cuts, abrasions, sores, bumps, etc. should be brought to the attention of the veterinarian.
Finally, bad breath - if bad enough - can cause a terrible smell to permeate around the whole dog. Daily dental brushings combined with healthy chew snacks and yearly dental checkups (for scrapings) are a must. However, if a Boxer has a bad breath issue, those brushings will not fix an established dental issue.
A cracked or abscessed tooth may be the cause and this most certainly needs to be treated professionally. Left untreated, infection can spread into the bloodstream and there most certainly will be the eventual loss of the tooth which can cause problems with ability to chew properly.
With minor breath issues, offering some healthy snacks to combat smelly bad breath is easy and effective. An example of a healthy treat that works well to clean plague and freshen breath, with healthy toffee extract and one that works via spearmint, parsley and fennel are: