If you mean raw wool, it often depends on the level of care by the farmer. Some shepherds I know wash their sheep regularly – well, more than once – while the fleece is growing, others don’t bother. Imagine you wore the same sweater for a year: you sleep in it, you exercise in it, and once in a while you stand in the rain in it. It would stink, right? Same deal when that sweater is still growing on the sheep, except the sheep also poop and roll in mud in their fleece.
Lanolin, a thick yellowish grease with a strong smell, is another source of the sheepy odour. Different breeds have differing levels of lanolin, and there can be wide variations within a breed depending on grazing, age, sex, whether a ewe has lambed that year, etc. Some mills remove some or all the lanolin, while others make it a point of pride to retain as much as possible. I personally don’t find lanolin to be an offensive smell, and it doesn’t bother me to work with wool ‘in the grease’. Lanolin is a component of many moisturisers, so it’s lovely for my hands. My mother won’t let me in her house if I’ve been working with greasy wool, though – the smell gives her the dry heaves.
A third source of smell is urine. Specifically, horses’ urine, if I recall correctly, though I’d imagine any large, regular source, such as cattle or human, would do at need. Historically, stale urine was the go-to cleaner for raw wool, and the finest tweeds were dyed using urine as a mordant (fixative). While these have largely been replaced with manufactured chemicals, urine-cleansed or mordanted wool can give off a distinct whiff of wee when damp, or if the wearer gets a little sweaty. It is alleged that the British House of Lords, where a substantial number of the Hereditary Peerage wear their historical tweeds, often honks like a dunny in the sun.
Originally posted on Quora.