The uncomfortable prickling sensation many people experience when wearing wool is known as “prickle.” This irritation often leads to the mistaken belief that one has a wool allergy, but the reaction is typically physical, not immunological. The primary factor determining whether wool feels soft or scratchy is the thickness of its individual fibers.
The Primary Cause: Fiber Diameter
The physical mechanism that causes wool to itch is directly related to the diameter of the individual wool fibers, measured in microns (one-millionth of a meter). Coarse fibers are stiff enough to poke the skin’s surface and mechanically stimulate pain receptors (C-fibers) responsible for transmitting itch and pain. This physical prodding creates the characteristic prickle sensation.
The threshold for comfortable wool is a fiber diameter below 30 to 32 microns. Thicker fibers are stiff enough to bend back and irritate the skin, triggering discomfort. Finer wool fibers (18 microns or less) are too flexible to penetrate the skin’s outer layer with enough force to activate these nerve endings.
A garment’s comfort is not based solely on the average fiber diameter, but also on the percentage of fibers that exceed the prickle threshold. Even fine wool can feel itchy if it contains a small number of coarser fibers, sometimes called “objectionable fibers.” The density of these coarse fiber ends protruding from the fabric surface determines the level of irritation a wearer experiences.
Distinguishing Physical Irritation from Allergic Reactions
The discomfort caused by wool is a form of irritant contact dermatitis, which is a physical reaction, not a true allergic reaction. Irritant contact dermatitis is characterized by the mechanical stimulation of skin nerve endings by stiff fibers, not an immune system response to the wool protein itself.
True immunological allergy to the wool fiber is rare. However, skin reactions can be triggered by residual substances from the manufacturing process, such as dyes, processing chemicals (like formaldehyde or chromium), or lanolin that was not completely removed.
Modern processing techniques have made allergic contact dermatitis from these residues unlikely in contemporary wool garments. If a reaction is suspected, wear a thin, protective layer between the wool garment and the skin; if the irritation disappears, the reaction is likely due to fiber coarseness, not an allergy.
Selecting Wool for Comfort
The animal source of the wool plays a large role in determining fiber diameter and comfort. Wool from the Merino sheep is popular for next-to-skin wear because its fibers naturally fall into the finer range, often below 22 microns. Superfine and ultrafine grades of Merino wool can be as fine as 15 to 18.5 microns, which most people find comfortable.
Other fibers from different animals possess fine diameters. Cashmere, sourced from goats, is renowned for its softness because its fibers are typically less than 19 microns thick, often reaching as low as 15 microns. Alpaca fiber is also regarded for comfort; its scales are smoother than sheep’s wool, which contributes to a less prickly feel.
When purchasing, looking for the micron count on the label is the most reliable way to predict comfort. For maximum softness, aim for wool products labeled as superfine or ultrafine, or those with a stated fiber diameter below 19.5 microns, as this range is comfortable for most individuals.
Strategies for Reducing Prickle
If wool garments feel too scratchy, several at-home methods can reduce the prickle sensation.
At-Home Methods to Reduce Prickle
- Conditioner treatment: Hair conditioner contains softening agents that coat and smooth the wool fibers. Soak the garment in a solution of cold water and a small amount of hair conditioner for about 30 minutes before rinsing.
- Vinegar rinse: This helps dissolve residual soap or detergent buildup that can make fibers feel stiff. Mix about a half cup of white vinegar with cold water, soak the garment for 15 to 20 minutes, and follow with a thorough cold water rinse.
- Freezing technique: Place a dry wool garment in a sealed plastic bag and leave it in the freezer overnight. The extreme cold is thought to temporarily stiffen and set the protruding fiber ends, making them less abrasive when worn.
- Wear a base layer: Wearing a smooth, thin base layer made of silk or cotton underneath the wool creates a physical barrier, preventing the prickly fibers from making contact with the skin.