This answer, while technically correct, is horribly incomplete. I would assume that the majority of people researching this topic are NOT in South America. This is important because that is the only place the chigoe flea is found. It should also be pointed out that the Chigoe flea attacks the feet primarily. So if there is evidence of sub-dermal infestation and you live outside of Brazil and Peru you almost assuredly DON'T have Chigoe fleas.
The fleas hop onto them and burrow in.
yes
Scabies
Scabies.
Yes, jiggers are parasitic sand fleas that can burrow into the skin of humans and animals, typically targeting the feet. Once embedded, they lay eggs which can cause infection and discomfort if not treated promptly. Proper hygiene and wearing protective footwear can help prevent jigger infestations.
No. Pubic lice don't burrow under your skin.
Scabies is caused by mites which create tunnels under your skin which are easily noticeable after they lay their eggs, the process of them hatching is what causes the itching, fleas don't burrow and only bite to cause a more or less harmless infection which itches if given attention.
Scabies is a skin condition caused by the mite Sarcoptes scabiei burrowing under the skin. It causes intense itching and a pimple-like rash. Treatment typically involves prescription topical medications.
razor blade beetles
Fleas are insects that jump and feed on blood, causing itching and discomfort for pets. They can also transmit diseases. Mites are tiny arachnids that burrow into the skin, causing irritation and skin problems. Both pests can infest pets, but fleas are more mobile and visible, while mites are often harder to detect and treat.
Are you sure you have fleas under your skin? If you do, you are the first person in the world to have them there. You may have some other parasite living under your skin, but it is not a flea. Fleas live on your skin where they bite you. They suck your blood. However, they do not stay on you. They spend 90% of their time on your bedding. You need to wash yourself, the clothes you sleep in and your bedding. Fleas also come with animals. They need flea control on their bodies. They need their bedding changed. And the floor of your house needs to be treated with insecticide. This will continue. The fleas will continue to live in the yard for 18 months. If you actually have a parasite under your skin, you will need a drug to get rid of it.
No, head lice live in the hair, by grabbing onto it. They can be anywhere in your hair, crawling up and down hairs with their grabby legs, but they must come down to the scalp to feed (suck blood) several times per day. They can not burrow into skin.