The difference between pain and suffering

I find it surprising how often the words pain and suffering are used interchangeably, as it often happens when discussing issues of animal welfare. The concept of suffering has profound implications when applied to both humans and animals, so we should examine carefully what it entails philosophically and scientifically.

Let’s consider pain first. When studying pain scientifically we need to make yet another distinction: that between nociception and pain. Nociception is the collection of signals in the nervous system that are triggered by an injury. These include the action potentials traveling in the nociceptive fibers of the nerves, the spinal cord neurons that receive synapses from them, the spinothalamic tract and other pathways that send nociceptive signals to the brain, the nociceptive areas of the thalamus, and at the end of the pathway, the somatosensory cortex, the insula, and the anterior cingulate cortex 1-5. Somewhere along this pathway nociception gets converted into pain, but not always. A clear example of nociception without pain is general anesthesia. In this state all the nociceptive pathways remain functional but there is no pain because there is no consciousness 6. On the other hand, we can also stop both nociception and pain: using a local anesthetic on the site of injury would stop all the nociceptive signals arising from it and therefore the pain as well. Finally, there can be pain without nociception in some cases of “central pain” 7 and phantom limb pain 8, 9 where the pain originates in the brain itself in the absence of injury and signals in the nociceptive pathways. Hence, although usually nociception triggers pain, they are not identical phenomena.

A clear example of nociception without pain is general anesthesia

If during general anesthesia there is nociception but not pain, does this means that pain requires consciousness 6? This is an important question because then the issue of whether an animal can experience pain would depend on whether that animal is conscious or not 10. This is a difficult issue because there are many competing definitions of consciousness and we are far from understanding what it is. While we assume that higher mammals like dogs, cats and horses are conscious, extending consciousness to animals vastly different from us with small nervous systems, like insects or mollusks, poses a seemingly insoluble scientific and philosophical problem. In scientific research on pain physiology, it is generally accepted that pain presupposes consciousness. For that reason, in the past the use of the word “pain” when referring to animals like rats and mice used to be frowned upon. The correct term was “pain-like behavior” or “nociception”. But recently the assumption that rodents feel pain has become increasingly accepted in scientific literature.

Modern definitions of pain skip references to consciousness. For example, the International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Another medical definition of pain is “an unpleasant sensation that can range from mild, localized discomfort to agony; pain has both physical and emotional components; the physical part of pain results from nerve stimulation. However, somehow the fact that the experience of pain is a conscious one is implicit in these definitions.

The fact that an animal reacts to injury cannot be necessarily be taken as meaning that it experiences pain; we could just say that it has nociception. For example, we could design an android with a simple electronic mechanism that makes it scream when we injure it, but we would never say that it feels pain. It’s just an automaton. If we change the electronic circuitry of the automaton for a simple nervous system like the one of a jellyfish or a worm, we would get an animal with nociception but not pain. Humans also display automatic responses to noxious stimuli while under general anesthesia, for example, their heart rate goes up when the surgeon cuts into them. However, we know that they feel no pain. If we take any reaction to injury as a sign of pain, then we would need to conclude that plants and even bacteria feel pain, because they have definite reactions to noxious signals. In conclusion, feeling pain requires at least some form of consciousness, while nociception is any response to harmful stimuli.

What about suffering? How is it different from pain? Clearly, the two concepts are far from identical because we can find examples when one occurs without the other. There can be pain without suffering; the example that first comes to mind is that of sexual masochists who derive erotic pleasure from some forms of pain. But one doesn’t need to be a masochist to experience pain without suffering. A lot of people enjoy spicy food, which basically induces burning pain in the mouth because capsaicin (the chemical responsible for the pungency of these foods) activates the TRPV1 channel, the initiator of heat-induced pain 11. Another example is that of athletes and other sports enthusiasts, who learn that pain is part of their favorite sport. Runners, bicyclists, skiers, they all know that pain from muscular fatigue is a sign that the exercise is being effective, that their muscles will grow as a result. “Feel the burn”, they say. Rock climbers like me know that jamming our fist in that crack will be painful, but that’s what is required by that technique 12. Pain is part of the sport and we learn to welcome it.

Venn diagram of pain, suffering and nociception JPG

And, of course, there can be suffering without pain. In fact, most of our suffering has nothing to do with pain. It is induced by negative emotions like sadness, shame or guilt, or by situations like deprivation of freedom, loneliness, distress, depression, empathy, social rejection, oppression, etc. Like its opposite, happiness 13, suffering is neither a sensation nor an emotion, but a state of being that encompasses the whole mind. The importance of understanding suffering cannot be overstated. Avoiding or lessening suffering is one of the major goals of our lives, and therefore it has a tremendous social and political significance. In view of that, it is strange that we don’t allocate more resources to research on suffering. We do investigate sources of suffering like disease and hunger, but it is also clear that a lot of suffering is internally generated. This should be better understood.

There is a big push from different ideologies to attribute suffering to animals, on the one hand, and to human embryos and fetuses, on the other. Also, thinkers like Sam Harris wonder whether artificial intelligences (AIs) would be able to suffer and even whether this should become a moral imperative not to bring conscious AIs into existence. Apart from the dogmatism involved in the different ideologies, answering these questions is hindered by how little we know about suffering. But we do know a few things. First, if pain requires consciousness, suffering doubly so. There cannot be suffering if there is nobody experiencing it, no awareness of it. Therefore, we cannot say that an animal, a fetus or an AI is suffering until we know that it is conscious 10. So in answering the question of whether animals are capable of suffering (or which animals are capable of suffering) we run against the difficult problem of consciousness. How can we know that a being completely different from us is conscious, has the same subjective experience of the world that we do? I believe that someday we may know enough about consciousness to answer that question.

I also think that when we do we will realize that consciousness is not all-or-nothing, but that there is a hierarchy of consciousness. Even in humans, consciousness increases gradually as we develop from embryos to fetuses, babies, infants and children, to become fully developed in adults. Likewise, some animals are more conscious than others –  in fact, we can be pretty sure that many animals (worms, jellyfish, sea urchins, clams, barnacles) are not conscious at all because their nervous systems are not large enough to support consciousness. If suffering requires consciousness, then this hierarchy of consciousness implies a similar hierarchy in the ability to suffer. There is a general intuition that this is the case. For example, if our cat has fleas we do not hesitate to kill the fleas to improve the well-being of the cat. This is because most people assume that fleas do not suffer while they do cause suffering to the cat. A similar moral calculation occurs in animal research when we choose the “lowest” possible animal species to do an experiment: a dog instead of a monkey, a mouse instead of a dog, a fly instead of a mouse. Moving downward in the scale of animal complexity, there must be a point where animal suffering must stop. Then, if we move upwards in the scale of animal complexity, human suffering must matter more than animal suffering.

This could also be deduced from the fact that a lot of things that make humans suffer are not present in animals: from human-specific emotions like guilt and shame to culturally-dependent situations like lack of freedom and exploitation. The ability to suffer may also be different amongst non-human mammals: apes, elephants, cats and dogs experience distress not only when in pain or deprived of food or water, but also in socially oppressive situations or when somebody they have bonded with goes away or dies – this type of social suffering does not seem to be present in mammals that live alone. These animals can suffer, but not in as many ways as we do, because our suffering is also triggered by things that animals do not experience, like lack of purpose and meaning in life, living in an ugly environment or being exploited.

Another puzzling fact is that humans are willing to accept physical forms of suffering to avoid mental forms of suffering or to obtain abstract rewards. For example, mountaineers are willing to endure life-challenging amounts of fatigue and deprivation to achieve the satisfaction of reaching the mountaintop 12. Or think of the hardship endured by people who fought for justice, liberty and against exploitation. Furthermore, animal consciousness is tightly woven to the present, whereas humans are able to suffer from things in the distant past and from dread of what the future may bring 14. The neuroscientist Antonio Damasio coined the term “extended consciousness” for the human ability to imagine ourselves in the future and remember how we were in the past 15, 16. Because of all these considerations, I propose to use the term “deep suffering” for the unique ability of humans to suffer in more profoundly meaningful ways than animals.

mountaineers are willing to endure life-challenging amounts of fatigue and deprivation to achieve the satisfaction of reaching the mountaintop

All this also implies that suffering cannot be separated from cognition and cultural heritage. Perhaps the deepest form of suffering is existential angst, a dissatisfaction that comes from consciousness itself. We know that we exist and we wonder what that means. Being happy or miserable depends on finding meaning to our lives. This quest for meaning is basically a cognitive endeavor encompassing our emotions, our ideas and the cultural environment that gave them to us. Animals do not wonder about meaning, they do not depend on an information-rich cultural heritage to be happy.

To summarize, suffering is not a mere sensation, like pain. Neither is it an emotion, like sadness or fear. It’s a state that encompasses our whole mind, that is made not just of negative emotions but also of thoughts, beliefs and the quality of our consciousness itself. Suffering, like its opposite, happiness, is a state of being. Perhaps, if conscious AIs become a reality in the future, their happiness and their suffering would be even more dependent on knowledge and culture than our own. For now, we should consider in awe how our unique consciousness is a blessing and a curse because it enables us to suffer and to be happy more deeply than it was possible before our species emerged from evolution.

Juan Carlos Marvizon


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  9. Iacono, R.P., Linford, J. & Sandyk, R. Pain management after lower extremity amputation. Neurosurgery 20, 496-500 (1987).
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  11. Loo, L., et al. The C-Type Natriuretic Peptide Induces Thermal Hyperalgesia through a Noncanonical Gβγ-dependent Modulation of TRPV1 Channel. The Journal of Neuroscience 32, 11942-11955 (2012).
  12. Bunting, C.J., Little, M.J., Tolson, H. & Jessup, G. Physical fitness and eustress in the adventure activities of rock climbing and rappelling. J Sports Med Phys Fitness 26, 11-20 (1986).
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  16. Damasio, A.R. The Feeling of What Happens (1999).


20 thoughts on “The difference between pain and suffering

  1. Yeah, I kind of had seen that about Steve Jobs before. I imagine that the many companies that had decided not to use animals do it in part for ethical reasons. We’re talking about sentient beings here. Definition of sentient being: A sentient being is one who perceives and responds to sensations of whatever kind – sight, hearing, touch, taste, or smell.
    Sentience: is the capacity to feel, perceive or experience subjectively. Eighteen-century philosophers used the concept to distinguish the ability to think (reason) from the ability to feel (sentience).
    Sentient ultimately comes from the Latin verb sentire, which means ” to feel” and is related to the noun sensus, meaning ‘feeling’ or ‘sense’.
    Animal cognition: Animal cognition describes the mental capacities of non-human animals and the study of those capacities.
    Animals like chimps and dolphins are famed for their intelligence. But new evidence reveals cleverness in creatures considered primevally dumb.
    The term Animal intelligence is currently used in three distinct but overlapping ways: as a synonym for animal cognition, to pose the question ” are animals intelligent?”, or to denote a discussion of relative levels of intelligence in different animal species.
    Humans top the list of the most intelligent creatures but cannot be underestimated the other members of the animal kingdom. Scientists say the definition of animal vs human intelligence is merely a matter of degree.
    Here is an interesting link

      1. But I have knowledge of other natural remedies that have worked for people. You’re gonna have to counter how untrue those claims are.

        1. This kind of unscientific nonsense (please provide peer-reviewed scientific papers showing efficacy of non-medicinal natural remedies) KILLS people. It is irresponsible, dangerous and has no place on this site or any other.

  2. I have presentation on medical controversies, and i chose to present animal rights, the article i found here helped me a lot. i do not understand why people think animals should not be used in research, they are being hypocrite since they would not hesitate to kill a flee in other to save their cat discomfort.

    1. It cannot be compared to a flea that can be killed in seconds to animals subjected to painful experiments throughout all of their lives.

      1. Surely if you are arguing that animals are “innocent” (which is a nonsense, they are amoral – neither innocent nor guilty) then it doesn’t matter how they die – only that they die….?

        1. Still you can’t compare a flea ( an insect) that indeed would take nothing of time to die to an animal that is capable of feelings of sadness, joy, pleasure, anxiety, etc. And that unwillingly is subjected to years of trauma and terror supposedly for the benefit of mankind. As Martin Luther King said in his famous speech: “One day the absurdity of the almost universal human belief in the slavery of other animals will be palpable. We shall then have discovered our souls and become worthier of sharing this planet with them” And “There comes a time when one must take a position that is neither safe, nor political, nor popular but he must take it because his conscience tells him that it is right.” And “Injustice anywhere is a threat to justice everywhere”.

  3. Complimentary therapy is used many times and has been shown to be effective in dealing with both the physical symptoms as well as the emotional/psychological symptoms that impact people affected by cancer. For example, aromatherapy, reflexology and massage have been shown to aid relaxation; relieve stress and tension; improve quality of life; aid sleep; improving coping with side effects and reduce feelings of anxiety and depression. All of these makes for a more effective treatment.

    -Aromatherapy is the controlled use of essential oils to promote physical and psychological well-being.
    -Therapeutic gentle massage uses light touch and gentle pressure to ease muscle tension and relax the body.
    -Reflexology is the application of gentle pressure to different points on the feet, lower leg or hands to deeply relax the body.
    -Relaxation therapy uses techniques including breathing exercises, guided imagery and meditation to quiet the mind and induce relaxation.
    -Bach flower remedies are natural remedies which help to balance emotions and mood such as fear, anxiety, lack of confidence and tiredness to name but a few. Black flower remedies are also safe for children to take.
    -Bowen therapy is a technique where the practitioner uses thumbs and forefingers on precise points on the body to make rolling type moves which gently stimulates the muscles, soft tissue and energy within the body. These moves prompt the body to make the adjustments which help to re-balance, relieve tension and reduce pain.

      1. Many of us feel that animals are like children. Innocent and helpless. The author Temple Grandin says animals think like autistic humans. She should know.
        In her new book, ‘Animals in Translation: Using the Mysteries of Autism to Decode Animal Behavior’ Grandin examines the surprising similarities between an animal’s mind and an autistic mind- her own. “Autistic people,” she writes, “are closer to animals than normal people are.” This may sound like a cruel judgement, the sort of thing a cold hearted clinician would say, but it isn’t. It’s simply an acute observation, all the more important because it comes from an autistic person. Her autism Grandin suggests, puts her somewhere between normal human mentality and animal mentality, not as a matter of IQ but as a matter of perception and emotion.

  4. There are some companies that don’t feel that they need to rely on animal testing to advance research. Example: This company besides promoting prevention and early detection, they discovered that secondary breast cancers had an unusual arrangement of sugars on the cancer cell surface. So they do secondary breast cancer research with special interest in the sugar biology (glycobiology) involved.
    They fund research on:
    *How the body’s natural defences could be harnessed to design more effective treatments and ultimately a vaccine.
    *Design better tools for earlier diagnosis of secondary breast cancer to increase survival rate.
    *How diet and lifestyle increases or reduces the risk of secondary breast cancer.
    There was a Fellowship awarded which developed a new therapeutic approach for the treatment of cancer based on refocusing of the immune system to destroy cancerous cells.
    In response to a critical need for biological samples to study breast cancer, it was established and funded a collection of much needed clinical material from over 3000 breast cancer patients. They will support continued innovation in breast cancer therapeutics to advance their knowledge of the interplay between antibodies and development of secondary cancers, or metastases, in breast cancer patients.

    1. There is a whole lot of different research – some involving animals, some involving people, some involving neither. Scientists, companies, and the public take advantage of all this research – which combines to give us a better understanding of disease.

      So when your company finishes developing it’s new treatment to use the body’s defences to develop a vaccine, it is likely that new treatment will undergo vigorous tests in animals for safety and efficacy.

  5. You took a very knotty question head on with science and reason! Bravo to you! A big existential and ethical issue I had was that I came to the belief that human lives matter more than animals, and when push comes to shove, we come first. However, I do not believe that we are the pinnacle of all things, or that we have any entitlement to such a claim to importance without solid evidence and facts. Much of what we believe to be important is very subjective, and quite frankly, biased towards our terms since we’re the only ones who can think about it! Things like our cognitive abilities being unrivaled by our fellow animals, but then again, other creatures possess other gifts we do not have. I still feel it is unfair, like many religions do, to declare ourselves above animals altogether, a common push against accepting evolution and our inter-connectedness with all life. My justifications for treating humans, and other higher animals with more regard is exactly as you put it, the capacity for pain and suffering.

    Also, I feel, and this is not a scientific statement, but a subjective one, that in nature, it is the natural order for a species to preserve its own interests above other species. One species will not self-sacrifice its own welfare for another’s benefit. We I feel, are entitled to the same. Humans should look out for humanity first and foremost, before we help other creatures. Yes, some things we need to do will involve not putting ourselves first, like protecting habitats and not destroying the ecosystem, but that’s because what affects them, will affect us because we depend on nature. This however, in my mind falls under “enlightened interest”. Not to mention, the “deep suffering” we can experience puts us on the pinnacle when solely judging by pain and suffering without any bias or interest in humanity at all, like if aliens were tasked with ranking organisms by the capacity for suffering. Your arguments help me feel more sound in my justification for putting humans first. Unlike detractors think, this does not justify cruel treatment of other animals, just prioritizing who should get the most considerations, like the flea and the cat.

    The other extreme, is not letting a human be alleviated of pain and suffering, like in a terminal illness, when we wouldn’t dream of putting our animals through such misery! All because that “human lives are worth more than animal lives”. What irony!

  6. Many times animals are subjected to unnecessary misery and pain through unnecessary painful and torturous experiments. Science has supposedly advanced so much that there are many alternative methods to animal testing. 🐒🐁🐀🐰👍

    1. Did you read the article at all? It’s not about any specific studies.

      Science has advanced BECAUSE of studies on animals – it’s the reason we have so many treatments for cancer, why simple infections are no longer deadly, and why children born today have so many fewer deadly diseases than their counterparts 100 years ago.

      1. So in other words, having conquered so many diseases and illness means that there’s less need of animal uses in experiments. After 100 years of experiments and successes and nowadays with the technological and medical advances there shouldn’t be the necessity to employ the use of helpless and unwilling animals.

        1. Unfortunately, there are still many diseases which are currently untreatable. Researchers use a variety of techniques to understand the develop treatments including human studies, animal studies, tissue studies , computer studies and more – all of these are together necessary. The laws in most countries say that animals may not be used unless there is no other way to gain the information – yet studies continue because there is sometimes no other way.

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