Do hand sanitizers have a negative impact on the human immune system?

Question

Related:

• Which is more effective at removing germs, washing with soap and water or using hand sanitizers?
• Does regular handwashing with antibacterial soap prevent disease?

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I've run across some claims stating that the regular use of hand sanitizers by healthy people is not only ineffective, but that a "germ free" approach to life, in actuality, is potentially harmful to the human immune system. Here are some examples:

Also, the body’s best defense against disease agents is its own immune system. You keep the immune system primed by ALLOWING it access to disease agents. People who live in plastic bubbles never have a chance to develop immunities, so when disease agents inevitably get through the plastic wrap, the body has little defense. (source)

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Other studies suggest that ultra-clean environments and the persistent use of antibacterial soaps and hand sanitizers may inhibit proper immune system development in children. This is because inflammatory systems require greater exposure to common germs for proper development. (source)

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Killing off the friendly bacteria can damage our natural defenses against other infections. We definitely don’t want to kill off that bacteria. In regards to the bad bacteria, or the ones that can cause sicknesses, it’s not certain that its in our best interest to kill them either. There is considerable evidence that some exposure to bacteria in the environment is actually beneficial because it helps the immune system develop. Some studies have shown an increase in allergies and asthma in people who were raised in an overly sterile environment. (source)

Some summary questions:

• Does hand sanitizer use hamper immune system development/effectiveness compared to using soap (non anti-bacterial/microbial) and water (assume same frequency of use)?
• Is frequent hand sanitizer use correlated with a "hyperactive" immune system (allergy/asthma prone)?
• Is there evidence that germs/microbes/etc. on the hands have a significant part to play in a person's likelihood of getting sick when some larger future exposure occurs?

Answer 1

While it is nearly impossible to carry out an experiment on whether hand sanitiser usage will cause the immune system to misfire/fail, there have indeed been peer-reviewed experiments carried out on the fact that significant reduction in exposure to infections/antigens (a likely result of overuse of hand sanitisers) may result in a hampered immune system, which may lead to autoimmune diseases. This is known as the hygiene hypothesis.

Epidemiological data suggests that immigrants to relatively "clean" countries, such as Australia and the UK suffer from additional risk of autoimmune diseases. It has been suggested that living in a "clean" country increases the risk of developing autoimmune diseases, presumably due to the reduced exposure to microbes.

Among adolescents who were migrants to Australia, the prevalence of asthma symptoms was higher than that reported using a similar methodology in their country of origin. Asthma symptom prevalence was related to residence time in Australia.

Of course, correlation does not imply causation. Therefore, research has been done to associate the hygiene hypothesis on the molecular and cell biology levels.

On the molecular/cell biology viewpoint, it has also been shown that reduced exposure to bacterial endotoxins (a product of bacteria) was correlated an increase in hay fever and other autoimmune diseases.

Endotoxin levels in samples of dust from the child's mattress were inversely related to the occurrence of hay fever, atopic asthma, and atopic sensitization. Nonatopic wheeze was not significantly associated with the endotoxin level.

The introduction of lipoproteins found in bacterial cell walls into mice was also shown to reduce inflammation caused by allergic asthma in mice.

Mucosal administration of OprI at the time of allergen challenge suppressed eosinophilic inflammation in the airways, and this suppression was sustained after a second allergen challenge

There has also been some contradictory evidence on the hygiene hypothesis.

Serologic evidence of exposure to certain gastrointestinal pathogens (eg, hepatitis A virus) has been inversely associated with either allergen sensitization or asthma in some, but not all, recent studies. Although heavy infestation with certain parasites (eg, helminths) is protective against allergen sensitization, there is conflicting evidence regarding the relation between parasitic infection and asthma.

In conclusion, the hygiene hypothesis is certainly not a fully accepted scientific theory, but further research will likely shed more light on this.

Studies are elucidating that susceptibility involves genetic variants and environmental exposures, alteration of our microbiome and potentially large-scale manipulation of the environment over the past century. Many of the findings reviewed are preliminary and will need confirmation, but exciting new paradigms and hypotheses are emerging as a result of these preliminary findings.

Answer 2

The human immune system needs exposure to antigens (external organism that have entered the body) in order to function properly. The danger of using hand sanitizers excessively (especially in young children) is that the immune system does not get to experience as many antigens as it would without the use of sanitizer.

A simple graphic illustrates how the system works in principle:

Without the antigen present, the immune system is less equipped to deal with the threat. This becomes far more serious after the age of 30-35 when adults lose their ability to recognise new antigens in the body and must rely on previous recognised antigens. This is a major factor in the reason why the elderly are far more susceptible to infection.

The current advice is to expose yourself to as many antigens (safely) as possible, before you reach the ages of 30-35. Hand sanitizer compromises your ability to equip your immune system to deal with threats later in life.

• Beck, Gregory; Gail S. Habicht (November 1996). "Immunity and the Invertebrates" (PDF). Scientific American 275 (5): 60–66. doi:10.1038/scientificamerican1196-60. Retrieved 5 November 2014.