Snot is slimy, and for most, it's gross and not pleasant. But, for all the reactions that slime can provoke — disgust, pleasure, or fascination — we depend on our slimy secretions. We have snot for a reason, and that slime can protect us from cells and surfaces. For some, watching slime can even provoke feelings of relaxation.
Here are five things about snot that you probably didn’t know.
1. Where Snot Comes From
Snot (or mucus) is slimy because it contains a special type of protein — mucins. Mucins impart some useful functions. Not only have mammals retained mucins from evolutionary predecessors but also, our new mucins are always evolving — in a phenomenon called convergent evolution.
If a regular protein gene is altered with sections of chains of sugar–protein molecules, called repeats, new functions are acquired. Repeats with a lot of proline, threonine and serine transform a typical protein to a mucin because of the polypeptide structure that is formed. Sugars can easily attach to and branch off of these sites through glycosylation.
For example, MUC7 is a gene that is expressed abundantly in human salivary glands, but mice do not have the same gene. In mice, a different gene, MUC10, that has some similar functions appears to have evolved from a regular proline-producing gene.
2. Why so Slimy?
What we call “slimy” is the paradoxical property of viscoelasticity. Secretions with mucins — like snot (mucus) or spit (saliva) — are known for their oozing, slippery and sticky feel. In technical terms, this is called viscoelasticity. Mucus and saliva can act as lubricants to facilitate movement and act as difficult-to-penetrate barriers to protect cells and surfaces.
Viscoelastic materials have an inherently dual nature — they behave like liquid and solids— and how they flow or resist flow depends on temperature, the rate of strain and time. For example, a viscoelastic material can flow like a fluid, stretch like an elastic into a thin strand, and at some point break as if it were a solid. Thanks to the structure of mucins, with sections of protruding sugar branches, mucus adheres well to a lot of surfaces because different parts of the molecule chains have the ability to bind with electrically charged, neutral or even hydrophobic materials.
3. Positive and Negative Feelings
In a study that investigated which emotions were associated with 21 different textures, researchers found that slime could provoke fear and disgust, but also, happiness and surprise.
Touch is an important way for humans to process the physical world. And the processing of physical sensations, whether felt on the skin, in the mouth or emotional perceptions, can get intertwined.
The feel of slime even elicits autonomic psychophysiological effects (which are subconscious changes in the body related to the person’s emotional state). In another study, slimes with similar characteristics to those of body fluids and foods altered sympathetic (fight or flight) and parasympathetic (rest and digest) activity.
Foods like oysters and escargot — animals known for their mucus secretions — or okras and seaweed — plants that produce soluble starches (which are essentially chains of sugar molecules) are disliked or enjoyed around the world because of their gooey texture.
4. Sensory Responses
In certain people, the feel of a slimy substance evokes strong physiological changes, which is called an autonomous sensory meridian response (ASMR). Slime is often featured in ASMR videos — videos that are designed to evoke feelings of calm and relaxation. Anecdotally, those who have watched videos of slimy substances and felt the sensations describe them as oddly satisfying or oddly relaxing.
ASMR may also be similar to synesthesia — a condition where you can experience a sense through another, like color and sound, at the same time. But in the case of ASMR, we may be unable to keep the connections of sensory information received by the brain from an emotional response produced by the brain.
5. Emotional Connection
For some situations, it’s not the emotional response that’s important, it’s the emotional connection that it represents. When infants observe who is willing to exchange slimy secretions with one another, they can understand who is part of their inner circle, according to a recent study.
Researchers watched infants in this study to see how they reacted — where they looked and for how long — to simulated scenarios. They found that when young children observe behaviors like kissing or sharing utensils between people, they recognize that it defines a close or intimate relationship.
Young children also seemed to grasp the intricacies of social relationships — that a close relationship defined different obligations or expectations than friendship did. Children also seemed to understand that for a close relationship — like between siblings — one would respond to the other in distress but wouldn’t expect toy sharing to occur between them.
You probably wouldn’t expect snot to define these social boundaries, but as we’ve learned, it’s a slime with many qualities and functions.