The short answer is no, they are not poisonous to humans. But that doesn’t mean millipedes can’t inflict harm. Many species of millipedes have glands that can produce fluids which are irritating. These fluids can cause allergic reactions in people who might have sensitivities to insect toxins or insects themselves. A few species can shoot these fluids quite a few inches. Those who touch millipedes will detect a lasting odor on their hands. The insects’ fluid is unsafe if it comes in contact with the eyes. Therefore, it is best not to handle millipedes. If one has, however, handled a millipede, he or she should wash his or her hands thoroughly with soap and water until the smell has totally disappeared.
Millipedes are, however, considered poisonous to other insects. For this reason they are considered beneficial organisms in the environment. The liquid that they emit is poisonous. The substances concealed by them are caustic and can burn through the outer body of other insects as well as the skin of larger animals.
If you have a pet and are concerned about the millipedes squirting harmful substances, it is probably best to try to control the millipedes. It can be hard to distinguish between which ones are poisonous and which ones are not, so to be safe, it is best to control them all. Entrances around the house, including crevices or cracks, will need to be caulked. The poisonous fluids, though not lethal, can be dangerous, so it is best to control the millipede population around your home.