You should be cautious in extreme level if you own a small puppy.
If an owner uses a product, which contain cyphenothrin, then it causes problems for small breed dogs. Another similar chemical with similar effect is permethrin.
These 2 active ingredients can be found in the majority of topical flea treatments.
How to deal with flea in puppies?
It’s hard to deal with fleas on small breed dogs and puppies since you can’t use any commercial flea treatments. However, the best way to get rid of fleas on new born puppies is using daily, gentle flea combing.
You can use Bayer Advantage II Topical Flea Treatment for Small Dogs
weighs at least 3 pounds; it contains two active ingredients, one that eliminates adult fleas, and the second one prevents young fleas from maturing and growing.
Once your dog weighs at least 4 pounds. You can use K9 Advantix II for Small Dogs,
This product is one of the most popular flea treatments on the market.
Source: Flea Treatments For puppies and small dogs