Before I start droning on about what ASMR is, I want to specify that this phenomenon is relatively new (at least from a scientific point of view) and due to its nature, is difficult to research, as there isn't a ton of concrete information on it. I felt the need to research it to the best of my limited abilities, however, because it seems like an interesting concept.
Definition
ASMR stands for Autonomous Sensory Meridian Response and is a new-fangled term that describes the "tingles" that some people experience when they are exposed to certain stimuli. The typical stimuli associated with this term are ordinary things like getting your hair brushed, educational videos, or listening to a soft, monotonous voice.
What are these "tingles" of which you speak?
Now, you'll notice that I put the word tingles in parenthesis and there is a reason for that. If you go to research ASMR on the internet, a lot of articles (that I believe are deliberately trying to be attention grabbing) describe the ASMR phenomenon as a "brain orgasm", which I think is taking things a bit far. The tingles are more accurately compared to goosebumps by the more scholarly articles I was able to dig up. This concept of ASMR being sexual in nature can be debunked by using the various responses to this idea in the various articles' comment sections. While this is probably not the most scientific way to do this, it should be noted that of the people who claim to experience ASMR, almost all consistently claim that the feeling they personally experience are more like relaxation or a limb that fell asleep rather than sexual. There is a theory that the tingles that people who experience ASMR are connected to the part of the human brain that responds to altruistic attention.
What's altruistic attention got to do with it?
One of the theories I saw about why some people experience ASMR is based on the social grooming of primates. A study of talapoin monkeys showed that monkeys who were given an opiate showed a marked decrease in their grooming habits while monkeys who were given an opiate-blocker went crazy for grooming. This implies that the act of grooming, a gentle and calm process which benefits the receiver more than the giver, can provide pleasure. This concept can be applied to ASMR triggers like hair brushing/cutting and being given routine exams by a doctor (according the ASMR site I found, cranial nerve exams are a popular trigger for people who claim to experience ASMR). These acts are typically calm, gentle and benefiting the receiver, allowing the recipient to relax, which could result in the tingles. This theory concerning personal attention being connected to ASMR can be supported by the types of ASMR videos on Youtube.
I decided to attempt a teeny bit of research on my own on Youtube. I searched "ASMR videos" on the site and filtered by most views. The 20 highest viewed ASMR videos on Youtube had at least 1.2 million views, the highest amount of views being 8.6 million. Of the 20 videos, 11 of the videos were directed to the viewer, typically in a "role play" situation such as a spa or doctor visit. 6 of the videos were indirectly focused on the viewer and more focused on various sounds that could trigger ASMR, such as brush sounds or crinkling sounds. There was a ASMR parody video in the mix, but I included it because there were a lot of people in the comment section who claimed to experience ASMR that said that while the video was meant to poke fun at the ASMR phenomenon on Youtube, the beginning portion of the video actually was a pretty decent ASMR video.
Just chill out, dude...
Another trend I noticed in my Youtube research was 19 out of 20 videos were videos where the ASMRtist (this is apparently the proper term to describe a person who makes these videos) whispers softly to the viewer. According to another article I found on ASMR, this trend may relate to the effect that high frequency sounds have on the human ear. The gentle whispers in ASMR videos, according to the neuroscientist who was interviewed in another article I found, could be affecting the middle ear. When this happens, it triggers a relaxed state in regards to the heart. This part of the ear is also part of the human body's calming system. This is why babies will calm down to the sound of their mother's voices. This concept also may explain (if you ignore those viewers that are only there to look at close up shots of pretty girls' faces) why most of the ASMRtists who are popular on Youtube are female. Since female voices have a higher frequency, it might be easier for their voices to trigger the calming system.
So people get "tingles," so what?
Besides the fact that this phenomenon makes people feel good, there is some speculation that the concept of ASMR, if it's proven to exist, could have some scientific benefits. A professor of biopharmaceutical sciences from Shenandoah University believes that because ASMR could be related to the reaction that babies have when in contact with their mother, during which endorphins are released that create a feeling of safety, it might be possible to use ASMR to help patients who suffer adverse side-effects because they have to take high doses of medications. He believes that by using ASMR techniques, along with medication, it might be possible for the amount of medication to be reduced, thereby reducing the adverse side-effects.
Sources:
http://www.abc.net.au/radionational/programs/radiotonic/the-art-and-science-of-whispering/5672870
http://www.su.edu/blog/2014/12/17/professors-expertise-asmr-featured-various-media-outlets/
http://www.anthro.utah.edu/PDFs/journal_club/Dunbar11GroomingBondingHormones.pdf
http://www.disclose.tv/forum/autonomous-sensory-meridian-response-come-again-t90196.html
http://www.asmrlab.com/
http://www.asmrlab.com/common-asmr-triggers/