Toxicity

Alcohol abuse can damage our brains both during their early development, and later on in our adult lives.

Alcohol and brain development

Alcohol is a neuro-developmental toxin. This means that it can affect children’s brain development during both the pregnancy and breastfeeding stages.

If an expectant mother consumes alcohol, for instance, research suggests that it may lead to a number of problems in the unborn child, such as:Popova, S., Charness, M.E., Burd, L., Crawford, A., Hoyme, H.E., Mukherjee, R.A.S., Riley, E.P. and Elliott, E.J., 2023. Fetal alcohol spectrum disorders. Nature Reviews Disease Primers.

• Reduced IQ
• Impaired executive functions, including:
  • Attention
  • Memory
  • Reasoning
  • Problem-solving
  • Planning
• Delinquent behaviour
• Seizures
• Problems with the sensory system

Alcohol and brain function

In adults, dementia and alcohol abuse are closely connected. There’s a high prevalence of alcohol abuse in patients with dementia, at 9–22%, while rates of dementia in alcohol abusers are also high, at 10–24%.Ridley, N.J., Draper, B. and Withall, A., 2013. Alcohol-related dementia: an update of the evidence. Alzheimer’s Research & Therapy.

Two types of dementia are particularly associated with alcohol abuse:Tian, T.Y., Pescador Ruschel, M.A., Park, S. et al., 2023. Marchiafava-Bignami disease. StatPearls. Eva, L., Brehar, F.M., Florian, I.A. et al., 2023. Neuropsychiatric and neuropsychological aspects of alcohol-related cognitive disorders: an in-depth review of Wernicke’s encephalopathy and Korsakoff’s syndrome. Journal of Clinical Medicine. Akhouri, S., Kuhn, J. and Newton, E.J., 2023. Wernicke-Korsakoff syndrome. StatPearls.

• Marchiafava-Bignami disease
  • This mainly affects male chronic alcoholics
  • Its presentation is variable, but it can progress rapidly
  • The cognitive problems resemble diseases that affect the frontal lobe of the brain
  • It results in disinhibited and socially inappropriate behaviour, with emotional outbursts
• Alcoholic dementia, including Wernicke-Korsakoff syndrome
  • This is a vague category, which consists of various combinations of neurological disorders
  • They result in both poor memory and one of the following cognitive issues:
    • Aphasia (problems with speech)
    • Ataxia (problems with motor function)
    • Agnosia (problems identifying people or objects)
    • Difficulties with executive function (making plans, organising, and so on)

Research has suggested that for urban dwellers, air pollution may be a factor in any toxicity issues they have.

For instance, levels of black carbon in the air have been connected to decreased cognitive function, and there’s evidence for a connection between NO₂ exposure and decreases in memory-span.Zare Sakhvidi, M.J., Yang, J., Lequy, E., Chen, J., de Hoogh, K., Letellier, N., Mortamais, M., Ozguler, A., Vienneau, D., Zins, M., Goldberg, M., Berr, C. and Jacquemin, B., 2022. Outdoor air pollution exposure and cognitive performance: findings from the enrolment phase of the CONSTANCES cohort. The Lancet Planetary Health.

Bacteria, viruses, and parasites can all act as endocrine disruptors, and so disturb our hormonal balance. They can also create an inflammatory-immune response. In both cases, these effects can lead to mental health issues.

Bacteria

A number of bacterial species have been known to produce toxins, as part of their infectious effects.Ghazaei, C., 2022. Advances in the study of bacterial toxins, their roles and mechanisms in pathogenesis. Malaysian Journal of Medical Sciences.

Viruses

Some viruses act like toxins, by causing cell damage and death. Others damage our bodies’ ability to fight toxins, by damaging our white blood cells.Nourazarian, A. et al., 2025. The interplay between viral infection and cell death: a ping-pong effect. Advances in Virology.

Parasites

Parasites are organisms that live inside our bodies. They not only take for themselves the nutrients we’ve consumed, but they use them to produce toxins which are actively damaging to us.Ahmed, M. et al., 2023. Intestinal parasitic infections in 2023. Gastroenterology Research.

The range of substances known as ‘drugs’ is very wide, but whether they’re pharmaceutical or recreational, they share a common set of toxic effects.

Recreational drugs

Plant-based recreational drugs include:

• Heroin
• Cocaine
• Cannabis/marijuana

Synthetic drugs include:

• Amphetamines, including speed
• Methylenedioxymethamphetamine (MDMA), also known as ‘ecstasy’

One growing category of synthetic drug is ’Chemsex’ (‘chemical’ and ‘sex’) drugs. These include:Schifano, F., Bonaccorso, S., Arillotta, D., Guirguis, A., Corkery, J.M., Floresta, G., Papanti Pelletier, G.D., Scherbaum, N. and Schifano, N., 2025. Drugs used in “chemsex”/sexualized drug behaviour — overview of the related clinical psychopharmacological issues. Brain Sciences.

• Mephedrone
• Gamma-hydroxybutyrate (GBH or just ‘G’)
• Gamma-butyrolactone (GBL)
• Crystallised methamphetamine (‘crystal meth’)

Pharmaceutical drugs

Many different kinds of prescription and over-the-counter medication can affect our detoxification systems. They can overload the liver and kidneys, damage the gut, and disturb our hormonal balance, all of which can contribute to mental health issues.

These pharmaceutical drugs include:

• Antibiotics
• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Contraceptive pills and synthetic hormone replacement therapies (HRTs)
• Psychotropic medication

Pharmaceutical and personal-care products are also a major source of ocean pollution, which can in turn damage our environment and lead to further health issues. One study, for instance, found a large number of toxic substances connected to these products around the Antarctic coast.Emnet, P.J., Gaw, S., Northcott, G., Storey, B. and Graham, L., 2015. Personal care products and steroid hormones in the Antarctic coastal environment associated with two Antarctic research stations, McMurdo Station and Scott Base. Environmental Research.

Both recreational and pharmaceutical drugs can contribute to:Sinclair, J.M.A., Kalk, N.J., Kaar, S.J. et al., 2025. Evidence-based consensus guidelines for the pharmacological management of substance dependence: recommendations from the British Association for Psychopharmacology. Journal of Psychopharmacology.

• Intoxication, which can lead to violence/damage to ourselves or others
• Psychological dependence, which involves a state of reduced pleasure, unease, or anxiety when we stop taking the drug
• Other longer-term mental health symptoms, such as:
  • Insomnia
  • Hypomania
  • Anxiety
  • Psychosis
  • Depression

Contaminated food poses a risk to us all. Everyone eats regularly, and many of us don’t grow our own food or know exactly how it was produced.

There are a range of ways in which toxins can get into food. Different types of food are produced by different methods around the world, but there are some notable common issues:Ashraf, D., Morsi, R., Usman, M. and Meetani, M.A., 2024. Recent advances in the chromatographic analysis of emerging pollutants in dairy milk: a review (2018–2023). Molecules. WHO (World Health Organization), 2023. Dioxins and their effects on human health. Geneva: World Health Organization. Chen, T.C. et al., 2024. Estimated human intake of endogenous and exogenous hormones from beef in the United States. Journal of Exposure Science & Environmental Epidemiology.

• Non-organic foods can be contamined by pesticides and herbicides (see below)
• Dairy and fish products have been found to have high levels of hexachlorobenzene (a fungicide)
• Seafood can accumulate toxins from industrial pollution in the ocean
• Dairy, eggs, and processed meat products have been found to have unhealthy quantities of dioxins
• A few growth hormones commonly added to meat and dairy can (even in tiny quantities) alter the balance of estrogen and progesterone in some women
• Grilling and barbecuing meat may increase the risk of carcinogenic (cancer-causing) toxins being released

Fragrance, or perfume, is a key ingredient in many personal-care products.

It’s important to note that lots of different substances can be referred to as ‘fragrance’. It’s increasingly become a general, positive-sounding term for obscure chemicals.Rádis-Baptista, G., 2023. Do synthetic fragrances in personal care and household products impact indoor air quality and pose health risks? Journal of Xenobiotics.

Many of these chemicals are endocrine disruptors. If we absorb them through our skin, they can get into our bloodstream and affect our hormonal balance.

They can affect our levels of:

• Estrogen
• Progesterone
• Testosterone
• Cortisol
• Thyroid hormones
• Adrenal hormones

And they’ve been linked to some cases of:Ashcroft, S., Dosoky, N.S., Setzer, W.N. and Satyal, P., 2024. Synthetic endocrine disruptors in fragranced products. Endocrines.

• Breast cancer
• Prostate cancer
• Obesity
• Diabetes
• Thyroid issues (hypothyroidism, autoimmune thyroid diseases)

Heavy metal poisoning can contribute to hormonal and neurotransmitter imbalances. They tend to be found in tap water, pesticides, and certain foods such as fish.

Some common heavy metals are listed below.

Mercury

Mercury is found in large edible fish, such as tuna, swordfish, and shark. It’s also a key component of some dental fillings.

Mercury toxicity has been linked to several mental health issues, including:Chikhladze, T., Chikhladze, N., Gigiadze, M., Gabunia, L. and Gorgaslidze, N., 2023. Effects of mercury on human health. Junior Researchers. Paduraru, E., Iacob, D., Rarinca, V., Rusu, A., Jijie, R., Ilie, O.-D., Ciobica, A., Nicoara, M. and Doroftei, B., 2022. Comprehensive review regarding mercury poisoning and its complex involvement in Alzheimer’s disease. International Journal of Molecular Sciences. Wojcik, D.P., Godfrey, M.E., Christie, D. and Haley, B.E., 2006. Mercury toxicity presenting as chronic fatigue, memory impairment and depression: diagnosis, treatment, susceptibility, and outcomes in a New Zealand general practice setting (1994–2006). Neuroendocrinology Letters.

• Chronic fatigue disorder
• Alzheimer’s disease
• Depression

Mercury is an endocrine disruptor, and so it can cause severe hormonal imbalances too.Marín, S. et al., 2024. Mercury, natural fertility and outcomes of assisted reproduction: a systematic review. Reproductive BioMedicine Online.

Methylmercury

Methylmercury has been shown to affect our neuro-development, by damaging stem cells in the brain.

One study showed that children who were exposed to methylmercury showed developmental deficits by the age of 7, and hadn’t overcome that deficit by their mid-teens.Grandjean, P., Weihe, P., White, R.F., Debes, F., Araki, S., Yokoyama, K., Murata, K., Sørensen, N., Dahl, R. and Jørgensen, P.J., 1997. Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicology and Teratology.

Lead

Lead is commonly found in old pipes and household paint, as well as some contaminated foods.WHO (World Health Organization), 2026. Lead poisoning. Geneva: World Health Organization.

It can have very severe effects on our mental health:Reuben, A. et al., 2022. Childhood lead exposure is associated with lower cognitive functioning at older ages. Science Advances. Schneider, J.S., 2023. Neurotoxicity and outcomes from developmental lead exposure: persistent or permanent? Environmental Health Perspectives.

• Patients exposed to lead often have lowered brain volumes
• Exposure in early childhood is associated with reduced school performance and delinquent behaviour in later life
• There is no safe level of lead exposure: very low levels of lead can still be highly damaging to the brain
• Cognitive problems caused by lead exposure can occur a long time after exposure has stopped
• The effects of lead neurotoxicity are almost always permanent

Lead is an endocrine disruptor, and so it can cause severe hormonal imbalances too.Javorac, D., Baralić, K., Marić, Đ., Mandić-Rajčević, S., Đukić-Ćosić, D., Bulat, Z. and Buha Djordjevic, A., 2023. Exploring the endocrine disrupting potential of lead through benchmark modelling — study in humans. Environmental Pollution.

Arsenic

Arsenic is often found in poultry and rice. Because it’s used in pesticides, it’s also often present in non-organic produce.

It can have a range of different effects on our mental health:Tyler, C.R. and Allan, A.M., 2014. The effects of arsenic exposure on neurological and cognitive dysfunction in human and rodent studies: a review. Current Environmental Health Reports. 

• Chronic arsenic exposure can lead to issues with cognitive functions such as memory and behaviour
• It can also precipitate psychotic symptoms, such as delusions and hallucinations
• Prenatal and early postnatal exposure have been linked with cognitive deficits in children, which become apparent by the time they start at school

This is by no means an exhaustive list. Other common heavy metals include cadmium, radium, copper, and barium, all of which can have similar health effects.

Toxic substances are present in a number of chemicals we use around our homes, or in the workplace.

Below are some of the most common.

Toluene

Toluene is found in glue, paint, and petrol. Chronic toluene exposure can lead to cognitive and behavioural problems, because it crosses the blood-brain barrier easily, and can cause brain cell death.Casanova, J.P. et al., 2025. Toluene toxicity in the brain: from cellular targets to molecular mechanisms. Annual Review of Pharmacology and Toxicology.

Woodward, J.J. and Braunscheidel, K.M., 2023. The effects of the inhalant toluene on cognitive function and behavioral flexibility: a review of recent findings. Addiction Neuroscience.

Solvents

Solvents are often found in contaminated drinking water (see below), but many jobs also involve the heavy use of solvents.

Research shows that children with mothers using solvents at work (nurses, hospital workers, cleaners, hairdressers, beauticians) may be vulnerable to behavioural and psychiatric problems, from as young as the age of two.Tillaut, H., Costet, N., Monfort, C., Béranger, R., Garlantézec, R., Rouget, F., Cordier, S., Saint-Amour, D. and Chevrier, C., 2024. Occupational exposure to organic solvents during pregnancy and child behavior from early childhood to adolescence. Environmental Health.

Fire retardants

Fire retardants, also known as ‘flame retardants’, are found in foam, furniture, mattresses, and some clothing.Vaezafshar, S., Wolk, S., Simpson, K., Akhbarizadeh, R., Blum, A., Jantunen, L.M. and Diamond, M.L., 2025. Are sleeping children exposed to plasticizers, flame retardants, and UV-filters from their mattresses? Environmental Science & Technology.

They’ve been shown to damage brains in the early stages of development.Vaezafshar, S., Wolk, S., Arrandale, V.H., Sühring, R., Phipps, E., Jantunen, L.M. and Diamond, M.L., 2025. Young children’s exposure to chemicals of concern in their sleeping environment: an in-home study. Environmental Science & Technology Letters.

Formaldehyde

Formaldehyde is a chemical found in foam, fire retardants, wallpaper, mirrors, dyes, and other common household objects.WHO Regional Office for Europe, 2010. Formaldehyde. In: WHO Guidelines for Indoor Air Quality: Selected Pollutants. Copenhagen: WHO Regional Office for Europe.

It can contribute to a range of serious physical symptoms. Some of these, including breathing problems and gut issues, may in turn contribute to mental health symptoms.

Water-damaged buildings often have bacteria growing in them, with fungal elements. These are collectively known as ‘mould’.

The toxic substances produced by mould are known as mycotoxins. If you ingest them, your gut and/or sinuses can become damaged, and there may be a range of mental health effects:Hoxha, A., Abbasciano, M., Avantaggiato, G., Zappacosta, T. and Tricarico, D., 2025. Mycotoxins and neuropsychiatric symptoms: possible role in special refugee populations. Frontiers in Pharmacology. Ehsanifar, M., Rajati, R., Gholami, A. and Reiss, J.P., 2023. Mold and mycotoxin exposure and brain disorders. Journal of Integrative Neuroscience.

• Mycotoxins affect our capillaries’ health and permeability, meaning that we may not get enough oxygen to our tissues; this can result in:
  • Headaches
  • Light-sensitivity
  • Poor memory
  • Poor concentration
  • Exhaustion
• Mycotoxins increase the production of inflammatory cytokines, which have been linked to anxiety and depression
• They can cause a deficit in the process of DNA methylation, which means that our bodies become less able to repair their cells
• DNA methylation is also essential for the production of neurochemicals such as serotonin, GABA, dopamine, epinephrine, and norepinephrine, which regulate our moods

The overuse of pesticides, herbicides, and fungicides is a global problem.

Some of them are now banned in high-income countries, including the most toxic ones and the ones which accumulate slowest. Many, however, are still widely used in low- and middle-income countries.

These substances are used in residential, industrial, and agricultural environments, and tend to be found in:

• Non-organic fruits, vegetables, meat, poultry, dairy, grains (and so on)
• Tap water
• Substances brought indoors on our shoes

The symptoms of pesticide poisoning (to which herbicide and fungicide poisoning are similar) include:Rodríguez, A., Castrejón-Godínez, M.L. and Monterrosas-Brisson, N., 2025. Pesticides: environmental stressors implicated in the development of central nervous system disorders and neurodegeneration. Stresses.

• Headaches
• Fatigue
• Weakness
• Dizziness
• Restlessness
• Nervousness
• Moodiness

If the poisoning is acute, it can lead to lasting neurobehavioural deficits. These substances are able to disrupt our brain function, by altering the balance of our neurotransmitters.

For instance, atrazine (the most common agricultural pesticide) can decrease our levels of acetylcholinesterase, an enzyme involved in the production of acetylcholine. Low levels of acetylcholine have been linked with poor memory, anxiety, and depression; research has shown high levels of anxiety and depression levels in farmers who use these pesticides.Frengidou, E., Galanis, P. and Malesios, C., 2024. Pesticide exposure or pesticide poisoning and the risk of depression in agricultural populations: a systematic review and meta-analysis. Journal of Agromedicine. Frengidou, E., Galanis, P., Chatzimichael, K., Kioulos, E. and Malesios, C., 2024. Depression and pesticide exposure among male farmers in Greece. Journal of Occupational and Environmental Medicine. Ochoa-Meza, A. et al., 2019. Neuropsychiatric disorders in farmers associated with organophosphorus pesticide exposure in a rural village of Northwest México. International Journal of Environmental Research and Public Health.

Pesticides can also deplete the nutrient levels in plants, depriving us of their nutritional benefits and contributing to nutritional imbalances. These, in turn, may lead to mental health issues.Hernandez, L.E., Ruiz, J.M. and Carvajal, M., 2024. Plant nutrition challenges for a sustainable agriculture of the future. Physiologia Plantarum.

Petrochemicals are commonly found in petrol, and the vapour surrounding it at petrol stations or busy roads.

But this isn’t the only way we can be exposed to them. Other types of petrochemical, including parabens and DDT, can be found in household appliances and objects.

Many petrochemicals are xenoestrogens. This means that in women’s bodies, they can mimic the sex hormone estrogen. This may contribute to hormonal imbalances, which can lead to a number of mental health issues.

There are many different types of plastic chemical, all of which are toxic.

The three main kinds are:

• BPA (bisphenol A), found in water bottles, CDs/DVDs, and sports equipment
• Phthalates, found in cosmetics, detergents, and items made from PVC (polyvinyl chloride plastic)
• PCBs (polychlorinated biphenyls), found in coolants, industrial fluids, and carbon-copy paper

Studies have connected exposure to plastic toxins with developmental problems in children. These toxins can affect our levels of male and female sex hormones, affecting children in the womb and in infancy.Yang, Z., Zhang, J., Wang, M., Wang, X., Liu, H., Zhang, F. and Fan, H., 2024. Prenatal endocrine-disrupting chemicals exposure and impact on offspring neurodevelopment: a systematic review and meta-analysis. Neurotoxicology.

They’ve been connected to the onset of mental health symptoms including:

• Hyperactivity
• Irritability and aggression
• Anxiety
• Depression

Research has shown a strong correlation between smoking and mental health symptoms.

Smoking can introduce huge numbers of oxidants into the body, including the brain. This may lead to healthy brain fats becoming damaged. Cigarette smoke also contains large amounts of cadmium, which can lower our zinc levels.Nemer, M.M. et al., 2024. Tobacco cigarette smoking induces cerebrovascular dysfunction followed by oxidative neuronal injury with the onset of cognitive impairment. Journal of Cerebral Blood Flow & Metabolism.

Conversely, nicotine withdrawal has been shown to interfere with our serotonin levels, which can affect our moods, and also with the development of our brains in early adulthood.Reynolds, L.M. et al., 2025. Adolescent nicotine exposure and persistent neurocircuitry changes: unveiling lifelong psychiatric risks. Molecular Psychiatry.

Tap water varies considerably according to region, but in Western counties it’s usually safe to drink.

But it does contain varying degrees of chemicals, which can become toxic in high quantities, and are better filtered out if possible.

The two principal substances are:Jandova, J., Schiro, G., Duca, F.A., Laubitz, D. and Wondrak, G.T., 2024. Exposure to chlorinated drinking water alters the murine fecal microbiota. Science of the Total Environment. Taylor, K.W. et al., 2025. Fluoride exposure and children’s IQ scores: a systematic review and meta-analysis. JAMA Pediatrics.

• Chlorine
  • This is found not only in tap water, but in swimming pools and cleaning products
  • Excessive levels can be harmful for the bacteria in our gut, causing gut dysbiosis 
• Fluorine, and related compounds
  • This is commonly added to public water supplies
  • Excessive levels have been shown to cause an average IQ decrease of 7 points in children

Contamination or poor preparation can cause many other chemicals to enter our water supply. These can include:Levin, R., Villanueva, C.M., Beene, D., Cradock, A.L., Donat-Vargas, C., Lewis, J., Martinez-Morata, I., Minovi, D., Nigra, A.E., Olson, E.D., Schaider, L.A., Ward, M.H. and Deziel, N.C., 2024. US drinking water quality: exposure risk profiles for seven legacy and emerging contaminants. Journal of Exposure Science & Environmental Epidemiology.

• Trihalomethanes (THMs)
• Heavy metals, including:
  • Arsenic
  • Radium
  • Aluminum
  • Copper
  • Lead
  • Mercury
  • Cadmium
  • Barium
• Hormones
• Pharmaceuticals
• Nitrates
• Pesticides, herbicides, and fungicides

(For more on the potential effects of heavy metals and pesticides, see above.)

During the foetal stage and early infancy, the blood-brain barrier only gives children a partial protection against the chemicals taken in from the womb or the surrounding world. This is because our growing brains need a lot of nutrients, so the barrier needs to be ‘leaky’ to allow them to cross.Connor, K.L. et al., 2026. Maternal nutrition as a key determinant of placental and developing blood–brain barrier xenobiotic protective functions. The Journal of Physiology.

At these stages, children are particularly vulnerable to toxins. The developing nervous system, in particular, is at high risk of damage. Several neurodevelopmental disorders have recently been linked to toxic exposure, including:

• Autism
• Dyslexia
• Attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD)

Studies show that these disorders affect around 10–15% of births, and are believed to be increasing in frequency. Since genetic factors account for only 30–40% of all neurodevelopmental disorders, we’re now learning that enviromental factors, such as toxins, must be playing a key role.Carlsson, T., Molander, F., Taylor, M.J., Jonsson, U. and Bölte, S., 2021. Early environmental risk factors for neurodevelopmental disorders — a systematic review of twin and sibling studies. Development and Psychopathology.

Some neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, have been linked to toxic pollutants. The potential contributors include:Kulcsárová, K., Piel, J.H.A. and Schaeffer, E., 2025. Environmental toxins in neurodegeneration – a narrative review. Neurological Research and Practice.

• Heavy metals
• Solvents
• Chemicals from plastics such as polychlorinated biphenyls (PCBs)
• Pesticides such as DDT

Alzheimer’s disease is the most common neurodegenerative disease, and Parkinson’s disease is the second most common. They both, at different stages, affect our motor skills, cognitive function, and powers of speech.

Research is starting to show that environmental toxins may be linked to the development and progress of both of these diseases.Lefèvre-Arbogast, S., Chaker, J., Mercier, F., Barouki, R., Coumoul, X., Miller, G.W., David, A. and Samieri, C., 2024. Assessing the contribution of the chemical exposome to neurodegenerative disease. Nature Neuroscience. Lefèvre-Arbogast, S., Chaker, J., Mercier, F., Barouki, R., Coumoul, X., Miller, G.W., David, A. and Samieri, C., 2025. Current epidemiological and experimental evidence relating the chemical exposome to Alzheimer’s disease. Alzheimer’s & Dementia.