When heat meets emotion

When temperatures rise, our bodies work flat out to regulate our body temperature. But what happens to our mental state when we expose ourselves to the scorching rays of the sun? The link between heat, hormones and our emotional well-being is of great significance here. 

“The skin has its own endocrine system,” explains Nina Dalkner, Scientific Director at the university department for Psychiatry and Psychotherapeutic Medicine at the Medical University of Graz. Put simply, this means that the skin transmits hormones and neurotransmitters from the outside into the bloodstream. The hormones associated with sunlight and how they interact with one another is a highly complex process. According to Dalkner, vitamin D, melatonin, ACTH, β-endorphin and β-lipotropin are some of the key hormones in summer. Hormones act as the real driving forces, establishing the link between the heat, our bodies and their reactions.

Vitamin D, serotonin and a good mood

Vitamin D plays a crucial role in the body and is produced naturally when sunlight hits our skin. It influences a wide range of hormonal processes that can affect our mental state. In particular, it plays a key role in the production of the neurotransmitter serotonin. This neurotransmitter, in turn, plays an important role in regulating mood. It is a neurotransmitter involved in communication between nerve cells in the brain and fulfils a wide range of functions in the body. Colloquially, serotonin is also known as the ‘happiness hormone’, as it has a mood-lifting effect and supports the natural day-night rhythm.

Dwindling tolerance for frustration

However, alongside the mood-lifting rays of sunshine, summer also brings with it oppressive heat. The human body has to work particularly hard and operates at full capacity to cool itself down. The two main methods are, firstly, the familiar process of sweating, in which the sweat glands in the skin produce sweat that then evaporates on the skin’s surface. Secondly, the body also utilises vasodilation. This involves the blood vessels widening to carry more blood to the skin’s surface, allowing heat to be released and the body to cool down. Not only does this sound exhausting, it actually is. These processes drain the human body’s entire energy reserves, which is why we just want to get into bed. Some people might now suggest ‘just having a nap’. However, what sounds so simple turns out to be rather difficult for people who do not have air conditioning. Temperatures above 30 degrees have been shown to impair sleep, as the circulatory system has to work constantly to cool the body down and prevent it from overheating.

Just like the sun’s rays, the heat stimulates hormone production. “Studies have shown that in hot weather, there is an increase in the production of the hormone vasopressin (also known as antidiuretic hormone or ADH), which is linked to aggressive behaviour,” says Dalkner. This constant exhaustion, combined with circulatory-related sleep deprivation and the production of hormones such as vasopressin, leads to a negative outlook. We become irritated more quickly and our tolerance for frustration drops considerably. Psychologist Craig Anderson from Iowa State University in the USA also found in a study that people’s propensity for violence rises significantly at temperatures above 32 degrees.

The hormones of summer explained…

Vitamin D is produced by sunlight on our skin. It plays an important role in regulating neurotransmitters in the brain, such as serotonin. Serotonin is often referred to as the ‘happiness hormone’ as it regulates mood. A vitamin D deficiency – and consequently a serotonin deficiency – can lead to mood disorders such as depression. 

Melatonin, the so-called ‘sleep hormone’, is produced in the dark and tells us when it is time to sleep. Our melatonin levels are lower in summer than in winter, as the days are longer. The possible consequences of too little melatonin in the blood include difficulty falling asleep and a delayed sleep-wake cycle. 

ACTH is produced in the pituitary gland. Among other things, it regulates the production and release of cortisol in the adrenal cortex. Cortisone is released as part of the body’s stress response, which is why ACTH is colloquially referred to as the ‘stress hormone’. Elevated cortisone levels can cause us to feel tense, restless or anxious. 

β-endorphin is a naturally occurring opioid peptide produced in the body. It acts as the body’s own painkiller and neurotransmitter. β-endorphin is mainly produced and released in the pituitary gland. It can relieve pain, enhance well-being and have a positive effect on mood.

β-lipotropin (β-LPH) is a precursor hormone formed in the pituitary gland. It regulates fat metabolism and the mobilisation of fat reserves. β-lipotropin also influences skin pigmentation by regulating melanin production. In addition, it plays a role in modulating the immune response and regulating inflammation.

Text source: Nadja Riahi, Elena Anna Rieser and Maria Lovrić-Anušić, period., 26 June 2026