What is hygiene?

I’ve been doing a fair amount of work on hand hygiene since November, e.g. this piece on the economics of hygiene for the Hygiene Hub and some costing work for WHO/UNICEF. It bothered me that definitions were not clear, so I put together this Venn diagram. It aims to be a broad means of categorisation, rather than a comprehensive listing of all possible aspects of hygiene. I had domestic settings in mind, and other factors may be more important in other settings, particularly health care facilities. Please flag other resources on this definitional question in the comments below, if you know of them!

Hygiene

Within and beyond the WASH sector, “hygiene” has often been taken to be synonymous with handwashing. However, it is really a broader concept than this, but how broad? At the extreme end of the spectrum, hygiene is “the practice of keeping oneself and one’s surroundings clean, especially in order to prevent illness or the spread of diseases” (Boot and Cairncross, 1993). This aligns with the adjective hygieinos in Ancient Greek, meaning good for health (Liddell and Scott, 1889).

Taking the broad Boot & Cairncross definition, many behaviours and practices would fall within the scope of hygiene, including: (i) excreta disposal; (ii) use and protection of water sources; (iii) personal hygiene (e.g. hand hygiene, menstrual hygiene management); (iv) food hygiene (e.g. handling, preparation and storage); and (v) environmental hygiene (e.g. surface wiping, solid waste disposal, animal management).

Personally, I think including sanitation and water within hygiene is so broad as to be unhelpful. It is more typical to take a narrower approach. For example, UNICEF and WHO (2019) define hygiene as comprising “a range of behaviours that help to maintain health and prevent the spread of diseases, including handwashing, menstrual hygiene management and food hygiene”. Some studies also note face hygiene and bathing (Prüss-Ustün et al., 2019). You could argue for separating out other things like surface cleaning, toy cleaning etc. The various aspects are discussed in more detail by Curtis et al (2001) This and a suggestion from my colleague Karin Gallandat led me to separate out personal, domestic and food hygiene in the above diagram, but I am sure there are many other ways to cut it. More environmental aspects might be included, but then overlap with environmental sanitation (also ill-defined) would become more problematic. Another argument might be to include disease prevention behaviours such as wearing a face mask when exhibiting respiratory symptoms.

Zooming in on hand hygiene

The final definitional twist to note is that hand hygiene comprises not only handwashing with soap and water, but also handrubbing with alcohol-based hand rub (not technically “washing”). These WHO guidelines have lots of definitions along these lines. Ash can also be used as a last resort. For all your questions on rubs vs. soaps, see the Hygiene Hub, especially this piece. In short, soap is just as effective, relatively cheap, and more widely available by comparison to rubs – it is also more gentle on hands. However, the calculus is likely to be different in health care facilities where rubs are often considered more appropriate, for various reasons.

From an infectious disease perspective, focusing on clean hands (vs. other hygiene behaviours in the venn diagram) is warranted. Hand hygiene is likely the hygiene behaviour that makes the most important contribution to preventing faecal-oral disease and, annually, 165,000 deaths from diarrhoea are attributable to inadequate hand hygiene behaviours (Prüss-Ustün et al., 2019). However, food produce may be an important exposure pathway in many settings, and more evidence is needed on this (WHO and UNICEF, 2019).

Hand hygiene can prevent faecal-oral diseases by removing pathogens after fingers touch faeces (or things which have touched faeces) and before those fingers touch food, fluids, or the new host’s mouth. See the famous F-diagram below (Wagner and Lanoix, 1958). Human faeces might touch hands directly, before entering the environment (e.g. after defecation or child faeces management). Crucially, however, they are also transmitted indirectly once pathogens are already in the environment (e.g. surfaces, other people’s hands, animals and their faeces). Therefore, even with good water supply and sanitation services, pathogens can still circulate and hand hygiene is necessary to reap the full benefits of WASH.

[note – this post was updated after helpful suggestions in replies to this tweet – thanks!]