Contagion heuristic

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The contagion heuristic is a psychological heuristic which follows the Law of Contagion and Law of Similarity leading people to avoid contact with people or objects viewed as "contaminated" by previous contact with someone or something viewed as bad—or, less often, to seek contact with objects that have been in contact with people or things considered good. This can be simplified to the idea that appearance does not equal reality: our appearance of something contaminated may pose no actual harm. For example, we tend to view food that has touched the ground as contaminated by the ground, and therefore unfit to eat, or we view a person who has touched a diseased person as likely to carry the disease (regardless of the actual contagiousness of the disease).

The contagion heuristic includes "magical thinking", where even though irrational, well-educated adults will think that touching an object transfers their qualities ('essence') to it. Such as viewing a sweater worn by Adolf Hitler as bearing his negative essence and capable of transmitting it to another wearer. The perception of essence-transfer extends to rituals to purify items viewed as spiritually contaminated, such as having Mother Teresa wear Hitler's sweater to counteract his essence.[1]

Given the case that a subject is given a glass of juice with a cockroach in it, they will tend to reject drinking it due to the potential toxins and microbes that could be harmful to the subject's health. However given a glass of juice with a now sterilized cockroach in it (no germs), the subject is still likely to reject it due to this rule of thumb. This is because the offensive properties of a cockroach still get passed into the juice regardless of actual physical threat of harm as it is seen as contaminated, hence leading to irrational decision making.


The contagion heuristic can be separated into three categories:

1. Positive or Negative[edit]

The positive and negative contagion heuristic show whether an object/ person is perceived as contaminated in a good (positive) or bad (negative) way. Hence, this will affect the heuristic in terms of how the person affected will react: be unwilling to come in contact with the object or willing.

Negative contagion occurs when a seemingly negative object has or will come in contact with an object that you have or will be in contact with. For example, a brief contact of your food with an object seen as disgusting will render the object "contaminated" regardless of the actual implications to the object such as transfer of viruses. Hence this might lead to the irrational choice to not consume the food.

On the other hand, positive contagion occurs when a seemingly positive object has or will come in contact with an object that you have or will be in contact with. For example, if you are donating an organ to a person perceived as moral (i.e., Mother Theresa), you will be more willing to donate to her as opposed to a criminal (seemingly negative), even though donating to both will have the same physical impact. Here, this is an example of when an object you have been in contact with (organ) will come into contact with someone or something seen as positive.

In both these examples, contact is required as in the Law of Contagion however, this can also be applied to an object associated with another. For example, reluctance to come in contact with a plastic replica of an object perceived as disgusting (negative) even though there are no negative implications from touching it.

2. Forwards or Backwards[edit]

The forwards contagion heuristic occurs when an object you are about to be in contact with has been in contact with someone or something else seen as positively or negatively contaminated. For example, referring to the example as above, forward contagion occurs when you are now in contact/ about to consume a piece of food that has touched the ground.

The backwards contagion heuristic[2] occurs when something you own/have been in contact with comes into contact with something or someone else seen as positively or negatively contaminated. For example, the unwillingness to allow one's personal objects to come into possession of people who are disliked. Findings from Kramer and Block[3] show that consumers may be less willing to accept a high auction price for a teddy bear they were selling if the person buying was perceived to be of low moral quality (i.e., a sex offender) as opposed to high moral quality (i/e., a mother of a young child)

For the backwards contagion to be more effective the person should have owned it rather than mere contact.

3. Physical or Non-physical[edit]

There is a range of ways an item or person can become contaminated. These were grouped after testing the 'predicted purification potency'[1] which is the level at which the object can be 'de-contaminated' by an action: e.g. washing.

Physical sources:

  1. Physical Germ Model
    Carried by a living invisible entity.(i.e., Salmonella)
  2. Physical Residue Model
    (i.e., Dandruff, Sweat)
  3. Associative Model
    How much an object reminds you of something or someone

In the cases of 1 and 2, the predicted purity potency turned out to be highly similar. In both cases, they are effectively moderated by washing, especially in the case of source 2.

For the associative model, a change in the appearance of the object seemed to be highly effective. In this case, physical contact is not required (but is seen as more contaminated if it occurs[4]) for the object to be seen as contaminated and hence differs from the above two cases. However, it is distinguishable from non-physical models as there is no spiritual element.

Non-physical sources:

  1. Symbolic Interaction Model
    Interaction with something of symbolic importance (i.e., sacramental bread which for certain individuals is simply the combination of wheat flour, yeast, water and salt without it's contact with a holy person alike a priest)
  2. Spiritual Essence Model
    When the 'essence' of a person is transferred to an object or person by contact. (i.e., a jumper owned by Hitler is seen as negatively contaminated as his 'essence' has transferred and he is generally perceived as of low moral quality)

These non-physical sources of contagion are more difficult to erase than the above three physical sources however, they both tend to be effectively reduced by opposite valence contact; that is, an opposite but equal force. For example, to reduce the negative contaminants on Hitler's jumper, someone of high moral quality will be needed to counteract the 'essence'.


Anthropologists suggested a contagion heuristic or more specifically magic thinking when traditional societies were observed doing cultural practices such as transferring a person's identity (or soul) to inanimate objects such as fingernails and hair which were seen as highly "contagious". Furthermore, these beliefs continued to also include objects that had been in physical contact with the person.[5]

Whilst initially thought to only apply to traditional societies, further research by Rozin and Nemeroff showed that it could also be applied to Western societies. Observing that the contagion heuristic seems to only apply to humans, they created three routes of reasoning.

  1. A rejection of potentially offensive food We are unlikely to touch foods that elicit disgust in attempts to protect our health. (i.e., disgust towards uncooked chicken as it is seen as contaminated with potential harmful microorganisms like salmonella.)
  2. Illness transfer between humans Avoid touching a 'contaminated' ill person due to fear of getting ill.
  3. Support Relationships Positive contagion encourages highly intimate acts with people we see as positively contaminated such as family and lovers. (i.e., sexual intimacy which would otherwise elicit disgust without love and lust)

Hence, the contagion heuristic seems to be a pre-adaptation, that is it evolved to be beneficial to health and relationships, supporting the survival of our species, but now no longer serves a person in the current environment.


Critically analyzing this theory can lead to a couple of flaws.

  • Positive contagion is relatively weak and might just be an over-extension of the negative contagion principle. This is most likely due to the negative bias: that is, when given two cases, one of negative and one of positive of equal force, the negative case will have a greater impact.[6] As an old Russian phrase states, "A spoonful of tar can spoil a barrel of honey, but a spoonful of honey does nothing for a barrel of tar.
  • The associative model doesn't require any physical contact as stated as necessary in the Laws of Contagion, therefore can be seen as an alternative to contagion rather than part of it. For example, we are more inclined to consume food when the word 'natural' is involved regardless of the actual content; the positive contaminant of the word 'natural' is enough to alter decisions due to our associations with the word.[7]
  • Inattention. We don't tend to think about the interpersonal history of entities that we seen as contaminated. When we receive change in the store, we do not think of the long string of humans, no doubt some unsavory, who handled it previously.[1]


As the contagion heuristic is highly interlinked with disgust, we acknowledge that this emotion can be very personal, hence variation:


As the contagion heuristic stems from understanding that harmful microbes can exist in certain foods, this limits the extent to which children apply this heuristic. This is because the knowledge and understanding of invisible sources of contamination such as germs and how they spread or multiply are not understandable to young children. Studies have shown that at the age of 3-5, children begin to develop contagion sensitivity (degree to which someone knows if something is contaminated or not). Whilst they begin to acknowledge entities as negatively contaminated, they do not understand the biological reasoning until an older age.[8] It is also important to realize the role that institutions (i.e., schools), parenting, time and culture can play into this.

Culture and Religion[edit]

Cultural variation plays a large role into disgust as it affects what is seen as positive or negative and hence certain societies may react to different contaminants. For example, cultural traditions such as removing shoes upon entering a house is practiced by many Asian societies (due to negative contamination) however not by American societies.

A study by Rozin and Nemeroff shows that religious groups have their own rules on what is seen as contaminated. The experiment explored whether Jews following the Laws of Kashrut would consume kosher foods that had been in contact or association with non-kosher entities. The report showed that even when the food is only contaminated by similarity (i.e., vegetarian bacon) , most would deter from consumption. However, these problems can be controlled by creating rituals to decontaminate the food or setting limits on how contamination. In Judaism, the boundary of allowing non-kosher entities contaminate kosher food is 1/60th of the total volume of the contaminated good given the contamination occurs by accident.[9]

See also[edit]


  1. ^ a b c Griffin, Dale; Kahneman, Daniel (2002). Heurisitics and Biases: The Psychology of Intuitive Judgement. Cambridge University Press. pp. 211–213.
  2. ^ Rozin, Paul; Dunn, Christopher; Fedotova, Natalie (2018). "Reversing the causal arrow: Incidence and properties of negative backward magical contagion in Americans". Judgment and Decision Making. 13 (5): 441–450.
  3. ^ Kramer, Thomas; Block, Lauren (January 2011). "Nonconscious effects of peculiar beliefs on consumer psychology and choice". Journal of Consumer Psychology. 21 (1): 101–111. doi:10.1016/j.jcps.2010.09.009. ISSN 1057-7408.
  4. ^ Newman, George E.; Diesendruck, Gil; Bloom, Paul (2011-08-01). "Celebrity Contagion and the Value of Objects". Journal of Consumer Research. 38 (2): 215–228. doi:10.1086/658999. ISSN 0093-5301.
  5. ^ Nemeroff, Carol; Rozin, Paul (June 1994). "The Contagion Concept in Adult Thinking in the United States: Transmission of Germs and of Interpersonal Influence". Ethos. 22 (2): 158–186. doi:10.1525/eth.1994.22.2.02a00020. ISSN 0091-2131.
  6. ^ Rozin, Paul; Royzman, Edward B. (November 2001). "Negativity Bias, Negativity Dominance, and Contagion". Personality and Social Psychology Review. 5 (4): 296–320. doi:10.1207/s15327957pspr0504_2. ISSN 1088-8683.
  7. ^ Rozin, P. (2005-08-01). "The Meaning of "Natural": Process More Important Than Content". Psychological Science. 16 (8): 652–658. doi:10.1111/j.1467-9280.2005.01589.x. ISSN 0956-7976. PMID 16102069.
  8. ^ Siegal Michael; Fadda Roberta; Overton Paul G. (2011-12-12). "Contamination sensitivity and the development of disease-avoidant behaviour". Philosophical Transactions of the Royal Society B: Biological Sciences. 366 (1583): 3427–3432. doi:10.1098/rstb.2011.0036. PMC 3189351. PMID 22042919.
  9. ^ Nemeroff, Carol; Rozin, Paul (1992). "Sympathetic Magical Beliefs and Kosher Dietary Practice: The Interaction of Rules and Feelings". Ethos. 20 (1): 96–115. doi:10.1525/eth.1992.20.1.02a00040. ISSN 0091-2131. JSTOR 640452.

Further reading[edit]

  • Nemeroff, C., & Rozin, P. (2000). "The makings of the magical mind: The nature of function of sympathetic magic." In K. S. Rosengren, C. N. Johnson, & P. L. Harris (Eds.), Imagining the impossible: Magical, scientific, and religious thinking in children (pp. 1–34). New York: Cambridge University Press.
  • Jennifer J. Argo, Darren W. Dahl, Andrea C. Morales; Positive Consumer Contagion: Responses to Attractive Others in a Retail Context, Journal of marketing research, 2008, Vol.45(6), p. 690-701
  • Paul Rozin, Linda Millman, Carol Nemeroff; Operation of the Laws of Sympathetic Magic in Disgust and Other Domains, Journal of Personality and Social Psychology 1986, Vol. 50, No.4, 703-712
  • Jennifer J. Argo, Darren W. Dahl, Andrea C. Morales; Consumer Contamination: How Consumers React to Products Touched by Others, Journal of Marketing: April 2006, Vol. 70, No. 2, pp. 81–94.
  • Thomas Kramer, Lauren G. Block; Like Mike: Ability contagion through touched objects increases confidence and improves performance, Volume 124, Issue 2, July 2014, pp. 215–228
  • Savani K, Kumar S, Naidu NV, Dweck CS; Beliefs about Emotional Residue: the idea that emotions leave a trace in the physical environment, JPers Soc Psychol, 2011, pp. 684–701
  • Bower, Lennea, Peynircioglu, Zehra F., McCabe, Paula, and Parker, Scott. Sympathetic Magical Thinking in Decision Making: Differences for Animate and Inanimate Decision Targets (2014): ProQuest Dissertations and Theses. Web.
  • Paul Rozin, Sharon Wolf; Attachment to land: The case of the land of Israel for American andIsraeli Jews and the role of contagion, Judgment and Decision Making, Vol. 3, No. 4, April 2008, pp. 325–33
  • Kelly, D. (2013). ‘Moral Disgust and The Tribal Instincts Hypothesis,' Cooperation and Its Evolution, Eds. K. Sterelny, R. Joyce, Calcott, B, & B. Fraser. Cambridge, MA: The MIT Press, pages 503-524
  • Hejmadi, Ahalya,Rozin, Paul,Siegal, Michael; Once in Contact, Always in Contact: Contagious Essence and Conceptions of Purification in American and Hindu Indian Children. Developmental Psychology, Vol 40(4), Jul 2004, 467-476