What are the advantages of hand sanitizer over soap on a backpacking trip? Do they fulfill the same purpose?
What would you recommend for hand sanitization?
The two products have some commonality of use but a different focus. Both have their place.
Soap is used (as I know, you know) for cleaning - it removes contaminants that are hard or essentially impossible to remove by rubbing or scraping or by use of water alone. It essentially must have water to work and it needs water to rinse it away after it has done its job. It's use as a sanitiser is important but a secondary result of its main role. ie by removing material from your hands (or clothes or elsewhere) it also removes contaminants that may cause disease. Soap by itself does not kill germs very well - instead it removes them. If the water source used with soap is biologically contaminated, the final rinsing off of the soap may leave your hands looking clean but actually quite 'germ' covered. If you washed your hands with soap in a small stream where there was a dead animal carcass slightly up stream, or where the water was faecally contaminated, there is a good chance that they would look misleadingly safe and clean. You could carry the water you used for washing, or for final rinsing, but the former would be undesirable from a weight aspect, and carrying rinsing water introduces unusual cleaning patterns (wash in stream, rinse from bottle) and also incurs a weight and volume penalty.
Hand sanitisers deal with germs by killing them 'in situ'. They do not primarily remove biological contaminants but instead render them inactive. Depending on the sanitiser used they may be a good solvent as well, so may be useful to remove a degree of soiling. However, the volumes available and/or used are usually small and sanitisers such as ethyl alcohol tend to evaporate too fast to be used as an effective gross surface cleaner when used in small volumes. Because they do not need to utilise a local water source they are immune to the effects of local contamination. But if eg you had blood on your hands, or faeces, or had vomited, the sheer physical overload of contamination could render the sanitiser ineffective unless you used very substantial quantities.
So - the idea is to have both available, with soap as your primary cleaner, backed up by sanitiser where there was a clear need, or where you were uncertain. In most cases sanitiser is unnecessary. The hardy pioneers never had it (or, rather, they preferred to drink it) and even now, soap is often enough more a luxury item than a necessity for many hikers :-). However, there are occasions when sanitisers will keep you healthy, or alive, when soap won't. It's a good idea not to have to rely on hindsight to determine when these occasions may be :-).
A Parallel to backpacking
I have travelled quite a lot in Asia in recent years - cities and travelling rather than hiking. I try to ensure that I have a small bottle of sanitiser with me at all times - no exceptions if possible. And, I seldom use it. After you have used a few 'squatty' toilets in typical conditions, and then gone to eat a meal, with or without the availability of a water supply for washing, having sanitiser to hand (literally) becomes very attractive. Even when water is available for washing in such situations, the merits of using it can be uncertain.
Some dislike sanitisers because of the perceived (or actual) effects on skin, their lack of naturalness etc. Each must decide for themselves the merits of such concerns.
Types of sanitisers
There are two main types of sanitisers, alcohol based and chemical based disinfectants. (You can argue that alcohol is also a chemical disinfectant :-) ).
Alcohol (usually 60% - 85% Ethyl Alcohol, plus a gelling agent plus a bittering agent) will kill 99.9% or so biological contaminants on your skin in seconds. It evaporates without washing or wiping so leaves hands "guaranteed" low-germ if not actually no-germ. It's effect on the environment (apart from the part of the environment that you wipe it on) is minimal. Even poured on the ground or in a stream its effects would be extremely localized. A 1cc squirt from a pump bottle will clean two hands up to high wrist level if not actually visibly dirty. So a small 100cc bottle will be ample for most journeys.
An alternative which is gaining favour relatively recently is Benzalkonium Chloride. (Also answers to the names a "Quaternary ammonium salts", Lauryl Dimethyl Benzalkonium Chloride, and a few other similar names). This is the disinfectant of your childhood and of ever since. Look at the labels of disinfectants in supermarkets and you'll find it is used in about 90% of them. Also used as a carpet cleaner, swimming pool disinfectant and moss killer. And more. Used under a vast number of labels and for any applications.
A 0.1% solution (!) is said by those currently touting it to be as effective as alcohol (by federal certification) and as it leaves a thin residue on your hands it keeps on keeping on. Unlike alcohol. At low concentrations it is very person-safe and can be used in mouth washes and similar. At 10% - 50% range it's nasty if ingested (ask me how I know :-( )(I won't make that stupid and careless mistake again) but that is an unusually high percentage. Cheapest is in budget disinfectant bottles in supermarkets at about 2%. Water down as required. Very cheap if bought as above. Does not evaporate well (similar to water). Ecologically probably OK in streams etc. once diluted.
Soap is good for many things. Sanitiser is an excellent companion when squatty toilets or dead animals in your water supply must be dealt with.
Below BAQ = Benzalkonium Chloride / Quaternary Ammonium salts / ... etc.
Effect on bacterial level
Excellent report here:
They conclude that washing with soap is more effective than water alone BUT under their conditions reduction in bacterial count was to 23% and 8% initially. So, a reduction by a factor of 12 is useful BUT 1/12th of "too many bugs" is still "too many bugs" in many cases.
I'll try and post some stats later but, based on a manufacturers promo card graph that I have, use of sanitiser gives 99% kill on first use and if you repeat it N times you get most of the survivors killed each time, so results become superb rapidly.
I just carry hand sanitizer for three reasons
It's going to come down to personal choice, but when I'm backpacking weight and water are huge concerns (and water is weight).
All forms of soap are formed from a combination of natural ingredients. It's best to find soaps that are marketed as "biodegradable" or "natural" - these have the least complex chemical formulas and will be the most nature-friendly.
Soap is simple to carry and has many uses. Sanitizer, same.
I usually take just a bar of plain soap. It’s universal, can be used to wash hands or hair, shave, or wash the clothes. And plain soap is friendly to the environment. I guess that a special desinfection liquid has the advantage of not needing any water to work. I’m happy with the soap.