Unmyelinated C-fibers are a nerve fiber found in the skin that provide the sensation of itch. These fibers are not coated with a protective layer of myelin, like other forms of nerve fibers. The lack of myelin allows these fibers to transmit sensations more quickly than other types. If something irritates the skin and causes an itch, it stimulates the unmyelinated C-fibers, which send a signal to the brain. The brain processes this signal, providing the perception of itch.
Using the unmylienated fibers to induce itch is a questionable but potent way to create a sensation in the user. The problem with the use of the sense is how to ensure the itch is desired and is not overwhelming to those that experience it. Is itch a positive experience? In very moderate amounts, itch can be acceptable and maybe even pleasurable. By activating the sense, we can use it to provide a warning in cases that a silent but intense signal is necessary. This would be a more amplified signal to ensure the user senses the signal. Again, in most applications, we will want a weak to moderate activation of the sense of itch.
Most design does not accommodate itch as a sense, and it is usually avoided. However, to create a rounder, more full sensory experience, it is a possible tool to include in the design and the design’s development. In very small amounts, itch can be ignored or blocked out, however as it grows, the sense of itch can feel interminable. Although it is not pain, itch will give negative feelings and associations with overuse. So, subtle stimulation of the sense through a mist, temperature change, or application of a chemical can provide more than enough of the sensory experience. Furthermore, it will be necessary to provide a chemical or treatment to remove the sense–we do not want a design experience to be like getting poison ivy or chicken pox–we want it to be an instant experience that wears off very quickly to avoid irritating the user. This may be through the interface with a chemical applied to a paper, textile surface, or the skin, then a second chemical application subdues the experience. This needs to be resolved through the design process, through trial and error.
For better or worse, itch is never the sole sense that is provided in a design. If it were the only input, then the user would have a very monochromatic experience that relied on the lack or presence of itch in various amounts. The variation on the itch sense is limited, so the ebb and flow of the experience would need to be provided through activating an array of the fibers to produce the desired effect. A single location will create a near binary experience of itch or non-itch.
Most forms of design do not include the experience of itch, so it is not surprising to have a design without it. Instead, we should think about the absence of itch, which will provide a sense of relief in many, but it might also deaden the experience for the user if it is wholly ignored throughout a project or environment. In nature, the activation of this sense is a warning to avoid something.
With the activation of many itch locations on the body, we can provide levels of the experience, but also directionality. The increasing levels of itch can be mapped and correlate with some input in the world or in society. If we want to keep attention on an event or indices, this will up the ante on the user acceptance and judgement on the use of the sense. A very great itch could signal worse outcomes for the stock market. This is an indirect relationship, but we can also use a direct relationship, say in virtual reality with the representation of insects or a wool sweater your grandmother gave to you.. We are able to make the experience move around the body which will create a rounder experience. This can be used with other forms of touch, as well. Say we want to pull the user around, can we create an itch sensation on their back and then turn that experience off after the body has rotated? How would we do this? Through actuators or chemical interaction?
Adapting itch to an existing structure is complicated and possibly difficult. Although we have access to ways to activate, it might be better to look away from the building and focus on the elements that come into contact with the skin. These include wall surfaces and fixtures, but also should include clothing and furniture. We are not likely to touch the ceiling or roll on the floor, but we can be expected to sit in a chair or place our hands on a table while talking or reading.
Designing for itch will include variations of the amount of the stimulant, but it should also be about the absence of the sense. The designer must keep in mind that not everyone will want to experience this sense nor will they feel the effects without a high enough amplitude of the sense.