There are some cases where you either cannot pinpoint where the smell is coming from or it really does appear to be coming from the dog's entire body.
Pug smells after going outside -
This is not all that uncommon. The skin is constantly producing body oils. These work to keep both skin and coat healthy. However, over time these oils accumulate since oil does not evaporate. It is recommended to give a Pug a bath every 3 weeks since this seems to be the tipping point when too much oil is trapped beneath the thick coat and needs to be cleansed away.
If a Pug goes outside and smells bad after rain or even if there is some humidity in the air, the moisture mixes with the oils in the coat and this can produce a really bad smell that some refer to as 'dog odor'.
Therefore, this most commonly occurs when a Pug is one week or less away from his scheduled bath time.
Another possible reason could be if the dog rolled in feces or other sticky matter, however since most owners are keeping a close eye on their puppy or dog, this is less likely to be the cause of a mystery smell.
Prevention and treatment:
If the smell is really bad, you can give him a bath a bit early as long as you are using quality products that will not dry out the skin
or coat. Be sure to do a full body brush beforehand. If he has just recently had a bath (within the past 2 weeks), you can give the coat a good brushing.
This will do two things: It will lift the hairs on the dense coat, allowing the moisture to air dry as you brush.
In addition, the brushing will pull out dead hairs that are trapped close to the skin, which will be covered in the water/oil combination. Removing these hairs will often remove the odor.
When you brush, be sure to use a quality leave-in spray. This will not only protect the coat from picking up debris, but also offer a fresh scent that can last up to 3 days.