Scabies II

Remember how I got scabies last summer? Thankfully, there has been no reoccurrence and I'm still not clear on where I picked them up in the first place. As I mentioned in my first scabies post, I had some questions about scabies that had difficult-to-find answers. Here's what I came up with, from a combination of what I could find in the scientific literature and my background in physiology.



Is permethrin a poison? Is it toxic? 
Toxicologists use the saying, "the dose makes the poison". The best example of this is water, which can be considered a poison because drinking enough of it in a short enough timespan can seriously harm or kill you. Permethrin is poisonous to teeny tiny scabies at the dose used to treat human infestations, it is not poisonous to the person being treated if used as directed. Read the directions carefully and call your doctor or pharmacist with any questions. The Centers for Disease Control (CDC) states that permethrin cream can be used on children as young as 2 months of age.

Does permethrin get absorbed into the bloodstream? 

Short answer: no, not if used as directed.
Longer answer: The outer layer of skin is made up of dead skin cells and is called the stratum corneus, meaning "horny layer" in Latin, which implies the deadness of the cells and how they can just sort of get sloughed off like layers on an animal's horn. Scabies mites only burrow in this outer layer; they don't go any deeper. Permethrin also doesn't go any deeper than this outer layer of dead cells. It's part of what makes it so safe to use.

What are the best home remedies for getting rid of scabies?
There are no home remedies that will get rid of a scabies infection as well as being treated with medication from a doctor. If you'd like to try some feel free to google but you won't find any here because they simply aren't proven to work.

Why do I need to use permethrin cream at night?

It is convenient to put the cream on when you're going to be laying mostly still for at least 8 hours. It's less likely to rub off or be washed off cuz, you know, you're just laying there. Permethrin also degrades with exposure to light so, theoretically, this could be another reason. It needs to stay on for many hours to ensure it gets absorbed into the tough outer skin cells to get to as many of the mites as possible and night time is just the most convenient time.

Why don't you have to put permethrin cream on your face or scalp? 

Hey, if you wanna shave your head go right ahead but don't blame it on the scabies, they don't really hang out on kid or adult faces because the pH is not to their liking. In the elderly and babies, scabies can be found on the face and scalp because their skin pH is higher and more hospitable to mites. If the hairline and neck isn't treated in these populations, the scalp mites can be a cause of reinfestation but for the average Joe or Jane, it's not needed.

Why does the permethrin cream take so long to work? Eight hours, really? 
The scientific literature doesn't explain why it must be on the skin for 8-14 hrs, just that it does. It's likely the long treatment time increases the amount of absorption (ONLY in the outer layer of the skin) and also ensures the medication will come into contact with as many mites as possible.

Why do scabies itch more at night? Are scabies mites nocturnal or something?

Scabies infestations are highly associated with nighttime itching. So much so there is a paper out there called "Intense nocturnal itching should raise suspicion of scabies". But could I find a paper that explained WHY scabies itch more at night? Nope. The closest I found was a paper examining why, in general, itch is worse at night and they happened to mention scabies as one possible cause of night time itching.

The first likely answer is that at night we are no longer busy with other things so the itch is more difficult to ignore. There are also changes in the way our body does certain things based on time of day, called circadian rhythm effects. Some of these natural changes can contribute to increased itch. At night, our skin temperature increases and mite movement has been correlated to movement: higher temps = more movement. Our bodies also lose more water at night through the skin which can make it easier for the mites to burrow in - think about how things shrink up and contract when they get dried out like, say, sour cream that's been left on the counter for days. The components making up skin can shrink up a minuscule amount leaving microscopic gaps that mites can use to pry in. Finally, corticosteroids are naturally occurring hormones that are at their lowest levels at night. Corticosteroids are normally anti-inflammatory so lower levels may lead to increased inflammation and itchiness. 

Why are scabies associated with dirty places or people?

Scabies infestations are related to crowded places not necessarily dirty places. Nursing homes, prisons, dorms, and schools are all common locations of scabies outbreaks. In the United States and other developed countries, the biggest problem with a scabies infestation is the annoyance of itching and loss of sleep. In other countries, the risk of infection in the open wounds is a serious issue. Scabies themselves don't cause death but infection of the wounds created by the scratching can.

Can I give scabies to my cat/ dog/ mouse/ fish/ rat/ other cuddly pet?

Nope, scabies can't cross species which means the human form of scabies, Sarcoptes scabiei, can't survive on other animals. The opposite is also true, the dog form of scabies, Sarcoptes scabiei canis, popularly known as mange, can't survive on humans but can survive on cats.

My co-worker has scabies and I sat at the same lunch table with him. Am I infected?

Scabies are transmitted by skin-to-skin contact and VERY rarely through infested clothing or furniture. They can only crawl, not jump like fleas, so the skin-to-skin contact has to be at least 10 min... which is why it's often transmitted sexually. Not because the mites are on the genitals (though they do like to go there) but because of the closeness of the act. Sometimes the doctor will prescribe treatment for everyone in a household because of the close contact that families have even if they don't show symptoms.

References 

Fawcett, R. S. (2003). Ivermectin use in scabies. American Family Physician, 68(6), 1089–92.

Hurwitz, S. (1973). Scabies In Babies. American Journal of Diseases of Children, 126, 226–228.

Patel, T., Ishiuji, Y., & Yosipovitch, G. (2007). Nocturnal itch: why do we itch at night? Acta Dermato-Venereologica, 87(4), 295–8. doi:10.2340/00015555-0280

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Please note: I will no longer publish comments mentioning "treatments" for scabies that have not been scientifically and clinically proven to work. If you have or think you have scabies, please see a medical doctor and use only medically approved treatments. There are many "treatments" and home remedies out there that are very dangerous and unproven. 

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I am not a medical doctor, none of this is intended as medical advice, and I cannot diagnose you in the comments. If you are concerned about your health, please see your physician.