There are three different types of stress. Are you in control?

Summary: there are three main types of stress. Also, the brain triggers the release of stress hormones, such as cortisol, and reallocates energy to ensure survival. However, psychological stress can have a long-term devastating effect on the body and the mind.   


There is more than one type of stress and each one affects you in different ways. For a general definition of stress I encourage you to read my previous post: what is stress?.

Let’s go straight to the point. There are three types of stress:

1) Acute stress – an extremely stressful event that demands an immediate physiological adaptation to ensure survival (e.g. a person jumping to avoid getting hit by a car when crossing a street or an antelope sprinting from a hungry lion in a savanna).

2) Chronic stress – a prolonged period of pressure in which an individual has no control over the situation (e.g. a farmer with less food caused by a drought that devastated his crops).

3) Psychological stress – a sustained emotional perception that generates a feeling of anxiety or discomfort towards life events (e.g. parents divorce, death in the family, made redundant at work) or social disruptions (e.g. long and busy commutes, poor working conditions, beginning or end of relationships).

The good news is that the body can reasonably withstand adaptation for short-term emergencies, i.e. acute and chronic stress. The bad news, though, is that psychological stress creates detrimental effects on your body and mental health; it might start as flu or a bit of anxiety and depression symptoms. Ultimately, psychological stress could lead to ulcers and even cancer [1].

What happens in the body during a stress-response?

Both dwelling on a failed relationship and being chased by a lion can trigger the rapid mobilisation of energy from storage sites (e.g. fat cells, liver, muscles) and the inhibition of further storage [1]— a hallmark of stress-response. So, what does this mean?

Cortisol, a steroid hormone produced in the adrenal glands located on top of the kidneys, is released as a short-term adaptive solution to mobilise energy reserves (e.g. glycogen) Once there is enough energy converted into glucose, critical muscles (e.g. the legs to enable running form any threat) receive it as quickly as possible. The mobilisation process receives additional support by an increase in heart rate, blood pressure and breathing rate, all of which circulate nutrients and oxygen. So far, so good, right?

However, remember that the brain controls the allostatic mechanism and does not distinguish what sort of emergency the body goes through (why? read here). The brain assumes there is a threat and reallocates its energy accordingly. In other words, whichever area or organ is vital to keep you alive (at that very moment) will receive energy; otherwise, it will have to wait until there is no more threat. Psychological stressors, however, might take a long time to go away.

Therefore, the brain maintains a state of emergency and halts most long-term and energetically expensive body functions. For example, during stress, there is reduced tissue repair and no digestive process available. Imagine a stranger attacking you. There is no need to have your digestive system functioning as if you were about to have lunch. Honestly? What you want is energy redirected to your legs so you can run away as quick as possible. These shifts also explain why in emergency situations your vision gets heightened, whereas your bowel movements may hint you need to go to the bathroom—immediately!

Likewise, the sexual drive undergoes some changes (e.g. females are less likely to ovulate, whereas males have difficulty with erection). The bottom line shows there is nothing more important than survival, and psychological stress creates unrealistic threats for long periods.


What is your weekly routine? Make a list of potential psychological stressors affecting you. How long have theses stressors been around? Have you noticed any symptoms of anxiety, such as excessive worry and difficulty to sleep?


Stress is a complex topic and has been negatively affecting many people’s physiology and mental health. It is a crucial survival mechanism linked to the brain, which controls the allostatic balance and will do whatever it is necessary to keep you alive. However, psychological stressors may extend for long periods and eventually affect essential body functions. The brain continually prioritises and reallocates energy to ensure survival. Similarly, if you unexpectedly lost your job, then you would save money for food and mortgage, rather than spending on a fancy dinner (presumably!).


[1] Sapolsky, R. M. (2004). Why zebras don’t get ulcers.

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What is stress?

Summary: stress is an organism’s reaction to anything that shifts the body out of its allostatic state. More importantly, stress is a survival mechanism orchestrated by the brain. Stress responses have evolved to save you from external threats by adapting to different set points.


Stress is an exciting topic and it applies to every living being. Why? Because stress is a mechanism that evolved to keep you alive. As you might recall from my previous post: “Nothing in biology makes sense, except in the light of evolution” – Theodosius Dobzhansky.

Imagine you are about to cross a street and, suddenly, a bus is speeding in your direction. What do you do? One spontaneous reaction is to freeze and potentially get hit by the bus. A more likely reaction, though, is to immediately jump back attempting to save your own life. These opposite, instinctive and stressful reactions are usually referred to as the “fight or flight” response [1]. Contrary to popular belief, stress is also beneficial and often save lives.

Stats and data

However, as you might expect, stress is implicated in many diseases of the mind (e.g. anxiety) and body (e.g. ulcers). For example, a study [2] reported that 74% of the UK population has felt so stressed they were unable to cope or felt overwhelmed. As a result, 29% of participants reported they started drinking (i.e. as a behavioural effect), 51% felt depressed and 32% said they had suicidal thoughts (i.e. as psychological effects).

These data indicate that stress can slowly accumulate damage to one’s body and mind. Furthermore, learning about stress and raising awareness of its effects may alleviate the lives of many people, including yours.

Basic concepts

I have mentioned before, but it is always worth reinforcing key concepts. A working definition of stress refers to ‘an organism’s reaction to a stressor’. A stressor is a biological (e.g. a bacteria) or chemical (e.g. caffeine) agent, environmental condition (e.g. humidity) or external stimuli (e.g. the speeding bus) that shift an organism from its optimal physiological state [3].

For example, an adult’s normal blood pressure in resting-state should be between 90/60mmHg and 120/80mmHg. In the first example (the speeding bus), you would have had an immediate surge in blood pressure to ensure your heart beats faster and delivers oxygen to lower parts of the body.

As a consequence, your blood pressure indirectly produces energy to make you jump and avoid getting hit by the bus. Therefore, a higher blood pressure was not only necessary but also became the optimal level to prevent a tragic circumstance.

Conversely, during sleep, the average adult’s blood pressure is lower than it is during the day. This means that the body is capable of adapting to various setpoints, i.e. different optimal levels, amid changing circumstances in diverse environments.

In other words, the body makes changes according to its needs without any long-term damage (i.e. ulcers or cancer). This process is called allostasis [4] and it receives a significant influence from the brain. Hence, the link with neuroscience. The brain orchestrates the behavioural responses in anticipation of and, adaptation to any event (e.g. the bus speeding in your direction). Thus, in terms of definition, a stressor is anything that knocks your body out of allostasis.


Can you think of daily things that shift your allostatic balance? Make a list and try understanding why these factors have influence over you? I do not want to spoil the fun, but some examples might involve your work, family reunions, Friday drinks and so on.


This was an introduction to the concept of biological stress. This introductory post should enable you to read future posts in my blog and articles involving stress from a scientific point of view. Furthermore, you should practice to identify external events and stressors that shift your allostatic balance.

Next time I delve into different types of stress and how each of them affect your body.


[1] Fight or flight response – Wikipedia.

[2] The Mental Health Foundation (2018)

[3] Sapolsky, R. M. (2004). Why zebras don’t get ulcers.

[4] Schulkin, J. (2003). Allostasis: a neural behavioral perspective.

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Your response to stress may lead to depression — a gene vs environment analysis.

Summary: genetics and environment are not mutually exclusive in conferring risk factors for depression; the answer may come from the interplay between the two variables in your response to stress.


Depression is a disabling mental illness. According to the Diagnostic and Statistical Manual of Mental Disorders (5th edition), the most common symptoms of depression are sadness, fatigue and anhedonia (i.e. the inability to feel pleasure in pleasurable activities).

Moreover, depression profoundly interferes with a person’s life. It impairs the ability to function at school during childhood and in society during adulthood. In its severest form, depression can lead to suicide [1]. Globally, depression represents a public health challenge affecting over 300 million people, and by 2030, it will be the most significant cause of disability in the world (World Health Organization, 2017).

There is an urgent need to raise awareness as well as to educate people about the potential reasons leading to depression. One example is the response to stress (i.e. how your body physiologically reacts to a stressor), which receives influence from the interplay between genes and environment. Nevertheless, there are still one-sided arguments out there.

The social argument

 A researcher called David Buss designed a correlational study between participants’ self-report (i.e. what people say) and behavioural measures (i.e. what people do). He wanted to analyse mate selection (i.e. how people choose their partners). Buss reported a positive correlation between the two factors, which indicates that personality is often consistent with behaviour [2].  

Why is this relevant to stress and depression? If personality correlates with behaviour, then people who consistently live in a stressful environment and present sad mood are potentially depressed. In his study, Buss describes three mechanisms driving the positive correlation between personality and behaviour, which you may identify in people with depression:

  • Selection. The deliberate choice and gathering between similar people as well as avoiding those who are different (e.g. depressive individuals are more likely to seek depressive-like individuals). The selection mechanism also applies to the environment (e.g. depressive individuals are more likely to avoid energetic places, such as a party).
  • Evocation. This mechanism refers to individuals who unintentionally elicit specific behaviour from others. (e.g. depressive children evoke more attention from their parents; whereas active children evoke a strict parental control).
  • Manipulation. The unaware modification of surrounding environments to address one’s personality (e.g. depressive individuals may decorate their homes and workplace with darker colours).

These mechanisms and patterns seem obvious, but most of us are unable to notice them. Moreover, social studies that attempt to address biology-based disorder must be interpreted with caution. The combination of the three mechanisms do not offer certainty; it only increases the likelihood of developing depression. Correlation does not mean causation.

Therefore, social arguments alone are unlikely to provide a reliable and valid answer. One-sided analysis struggle to report normative measures enabling clinical treatment of depression (e.g. cognitive behavioural therapy). As a consequence, correlational studies are more likely to maintain the status quo, rather than providing a solution.

The interplay with genetics

Gene-environment interaction is the link between two variables arising from the effects of one variable changing conditional to the other.

Let me unpack this for you.

The interaction between your genes and the environment occurs when genetic factors influence the body’s responses to the environment (or whatever happens around you). The environment cannot directly alter gene sequences. However, genetic effects, such as the ability to cope with stress, are dependent on gene expression [3]. For example, the fight or flight response varies from one person to another.

Two factors influence gene-environment interaction:

  • Spontaneous mutations. Each person inherits 50% of genes from her mother and 50% from her father. However, along the process, there are genetic mutations that make you different from your parents. These include changes which you cannot ‘see’, such as the production level of gonadal hormones under a stressful state. So, let’s get used to thinking beyond ‘eye colour’.
  • Population changes. The changes in the frequency of a gene in a population. For example, a native tribe living in a remote location with no external interference is more likely to maintain similar characteristics. In this case, it creates a genetic bottleneck and some diseases never disappear from a population. Conversely, in a metropolis like London, there is more genetic variation.

Therefore, the environment you live in can relatively interfere with your genetics expression, mainly through your ability to cope and respond to stress.

Genetic triggers

King’s College London researcher Robert Plomin reports that the environment accounts for over 50% of the population variance of depression [4]. Thus, changes in the environment play a significant role in heritability compared to the role of genetic mutation alone. Below are some elements that affect your stress-response and increases the chances of depression:

  • Risk factors. Social and Economic Status triggers a stress response (e.g. worry and anxiety).
  • Social interaction. Parenting style, loneliness or a poor workplace environment.

In other words, it is likely that a person with a negative genetic predisposition to stressful reactions become depressed living in a hectic and chaotic environment. So, taking some time to identify stressful triggers in your environment as well as particular behavioural patterns may prevent mental illnesses, such as depression.

Despite the efforts to understand the overall scenario conferring risk of depression, one-sided analysis is not an effective way to solve the problem. Instead, an individual analysis would be far more effective. The interplay between genetics and environment is an insightful source of information. Your stress-response to the environment you live might be a key player in developing depression.


[1] Gunnell, D., Kidger, J., & Elvidge, H. (2018). Adolescent mental health in crisis.

[2] Buss, D. M. (1987). Selection, evocation, and manipulation. Journal of personality and social psychology, 53(6), 1214.

[3] Rutter, M. (2010). Gene-environment interplay. Depress Anxiety, 27(1), 1-4.

[4] Plomin, R., DeFries, J. C., Craig, I. W., & McGuffin, P. (2003). Behavioral genetics. American Psychological Association.

Lau, J. Y. F., & Eley, T. C. (2010). The Genetics of Mood Disorders. Ann Rev Clin Psychol, 6, 313-337.

World Health Organization (2017). Depression and other common mental disorders: global health estimates.

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Stress can save your life.

Summary: The understanding of evolution is key to all branches of modern biology. The interplay between replicators (genes), vehicles (the body) and the environment explains why some species have adapted to a particular environment and could not thrive somewhere else. Moreover, stress is what indirectly leads to adaptation. As a consequence, the organism might live long enough to reproduce. However, competition is a crucial condition of natural selection and eliminates species that do not adapt.

Nothing in biology makes sense except in the light of evolution.

Theodosius Dobzhansky (geneticist).


You are a product of natural selection. However, your response to stress contributes to whether you will continue to exist (by ‘you’ I mean your genes). The link between natural selection and stress might seem distant but allow me to take you through the facts.

There are two concepts to have in mind:

  • Genes, also known as ‘replicators’, are the primary unit of selection and heredity. Thus, in the process of reproduction, the genetic information will be duplicated and then passed on, forming 50% of your offspring (aka children).
  • A vehicle is the body protecting the genes (e.g. the human body, your dog’s body, a tree’s trunk and leaves or the cell membrane of a bacteria). Each species uses different vehicles to protect and pass on their genetic information. Some species (humans) can live in more than one type of environment; others cannot (that is why you do not find kangaroos in Alaska)

Let me unpack this for you.

Your parents’ genes contain the necessary instructions for your cells to produce particular proteins. These proteins will replicate some of their characteristics (e.g. height). These characteristics will form your body (i.e. the vehicle) and determine your chances of surviving, reproducing and passing on your genes in a given environment.

For instance, a bird with a fragile beak living in an environment where there are only hard-shell nuts is unlikely to thrive. Probably, stronger, larger beak birds can crack and eat those hard-shell nuts. As a result, these strong-beak birds will stay healthy and reproduce. Whereas, the fragile-beak birds will either die of hunger or adapt (e.g. eat something else). These possibilities (die or adapt) indicate there is an evolutionary pressure acting directly on the population of birds making them stressed. Researches, Grant & Grant, have reported a real example involving birds. The Galapagos finches (Geospiza magnirostris) has developed into three other species.

The bird example has a hidden message that applies to every species on the planet (including humans) and links stress with natural selection: there are limited resources available. The most critical resources are food, shelter and mating partners. The lack of resources, triggers stress (e.g. hunger) in each bird. Thus, each bird will seek new alternatives to survive by adaption (e.g. moving to a different area). Therefore, competition is a necessary condition for natural selection to exist, and stress is the body’s reaction to ensure survival.

The role of stress.

Stress is a survival mechanism characterised by “an organism’s reaction to a stressor”. Stressors shifts the organism (e.g. humans) from its optimal physiological state. There are several type of stressors:

  • A biological agent (e.g. a influenza virus).
  • A chemical agent (e.g. alcohol).
  • An environmental condition (e.g. hot weather)
  • An external stimulus (e.g. a being bullied)

A real-life example involves an adult’s average heart rate in resting-state, which is between 60-100 beats per minute. However, imagine you are walking home at night, and someone tries to attack you. What happens? Your heart rate will immediately increase. The up-regulated heart rate will ensure the delivery of oxygen to your legs, generating enough energy to start running and potentially avoiding the attack. Once you are safe at home, your body restores its stable physiological state, and you are no longer in stress. This case is a simple example of how stress works for you and enables a vehicle to pass on its replicator to the next generation. Scientists and writers often refer to this survival mechanism as the fight or flight response, a concept put forward by Walter Cannon in 1915.

However, there are ways in which stress works against you. For example, sustained psychological stress (e.g. a frustrating job) may develop into mental illnesses, such as depression. But there will be a post dedicated to psychological stress.

Key takeaways: Stress is key to ensure survival under natural selection. It can literally save your life. Also, stress is essential to evolution by adaptation. Hopefully, you will begin to view human behaviour from a scientific point of view, which offers several insights to your day-to-day life.


Dawkins, R. (2006). The selfish gene. 30th anniversary ed. Oxford ; New York: Oxford University Press.

Foley, R. A., & Lewin, R. (2013). Principles of human evolution. John Wiley & Sons.

Grant, Peter R., & Grant, B. Rosemary (2008), How and Why Species Multiply: The Radiation of Darwin’s Finches, Princeton University Press

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