A study found slower responses and lower accuracy on cognitive tests as temperatures rose, with the clearest differences at 40C. Poor sleep and stress can also contribute to brain fog, while memory complaints are common during menopause.
The researchers tested working memory and executive attention as temperatures climbed. At 40 degrees, they recorded the clearest differences in performance: responses took longer and accuracy fell. Published in August in Scientific Reports, the findings add evidence that intense heat can temporarily affect how people think.
Spain also had a September with temperatures above the usual levels, according to AEMET. Neuropsychologist Elena Martín Ferrer says heat can put extra strain on the body’s temperature-regulation systems. Dehydration may pile on that strain and affect attention or working memory. Processing speed may suffer too, as can decision-making.
Brain fog covers more than forgetfulness. A study published in February 2026 in Personality and Individual Differences examined the Brain Fog Scale, or BFS, a tool designed to assess the experience. Its authors describe brain fog as multidimensional. People may report difficulty concentrating or slower thinking. Others notice small memory lapses, trouble finding words or difficulty keeping several things in mind. Brain fog describes symptoms; it is not a diagnosis with one established cause.
Sleep and stress can also play a part. Adenosine builds up during waking hours and contributes to sleep pressure. Its levels fall during rest, helping restore alertness. Too little sleep can leave people drowsy and weaken attention and cognitive performance.
Other possible contributors include chronic stress and sleep apnoea. Cognitive complaints can also accompany some nutrient deficiencies or thyroid problems. Infections and certain medicines are further possibilities. Anxiety and depression can be associated with these complaints as well.
Menopause is another period when memory and concentration complaints are common. A review published by The Lancet in April 2026 examined cognitive symptoms during this stage. Paloma de L’Hotellerie-Fallois Armas, who directs a neuropsychology centre in Torrelodones, says these difficulties can be particularly disruptive for women of menopausal age and may prompt them to seek help. Data from the SWAN study indicate that about 60% of middle-aged women report memory problems during the menopausal transition.
Complaints can include forgetfulness or difficulty finding words. Trouble concentrating is another reported symptom. They may occur alongside hot flashes. Mood changes and sleep problems can accompany them too. The relationship between falling oestrogen levels and objective cognitive changes remains under discussion. Memory complaints during menopause do not by themselves indicate dementia.
Sleep disruption can add to the fog. Hot flashes and night sweats may cause repeated awakenings, leaving sleep less restorative and making concentration or memory harder the next day. Sleep, mood and hot flashes do not account for every cognitive change observed in research. Several factors can overlap.
Some people experience mental fog alongside psychological conditions. Neuropsychologist Irene Hyam Cuenca says it can occur with post-traumatic stress or dissociative symptoms. It can also accompany anxiety or depression. When factors overlap, it may be difficult to separate a cognitive symptom from fatigue, poor sleep or low mood.
Diet is under study too. A review published last April in Current Nutrition Reports examined possible links involving inflammation. It also considered the gut microbiota and sleep. The review was titled Nutritional Approaches to Managing Brain Fog. José Manuel Fernández-Real, a researcher at the Girona Biomedical Research Institute (IDIBGI), cautions that a digestive problem alone does not establish the cause of confusion or memory trouble. Gastrointestinal or metabolic changes may be associated with inflammation. They may also be linked to nutritional deficiencies or shifts in metabolites that could affect brain function.
If the problem persists despite changes to daily habits, worsens or significantly interferes with everyday life, the source recommends consulting a specialist. A clinician can assess cognitive symptoms and consider whether further evaluation is needed, rather than automatically attributing them to menopause. Paloma de L’Hotellerie-Fallois Armas also points to adequate sleep and regular exercise. A balanced diet may support cognitive function.
