Its predictability distinguishes SAD from other forms of depression

Roughly 10% of the world has SSAD—SAD’s milder, nonclinical cousin

Subsyndromal affective disorder is diagnosed when someone exhibits two of the nine major criteria for depression (but not more than five) as a result of seasonal changes. While it is milder than primary SAD, SSAD is still significant and impacts millions.

10 percent of SAD cases occur in the summer

Despite its significantly lower incidence, summer-risk SAD is as significant as its winter counterpart. Rather than being prompted by less light, the summer version is typically spurred by high temperatures, strong light, distinct summer time social pressures (appearing in a bathing suit, for example), and pollen. Common treatments include keeping cool and prioritizing sleep.

Winter-risk SAD is more likely in regions above 40 degrees latitude north

Using latitude, depression prevalence, and populations of women and those aged 18-30, this map shows the risk of experiencing seasonal affective disorder during the winter. Researchers weighted latitude most (50%) and demographics least (5% each for women and young adults). Overall risk is not a useful predictor of prognosis for an individual.

SAD 101 from the folks at NIMH—where the condition was first identified

Norman Rosenthal led the team at the National Institute of Mental Health that first identified and described seasonal affective disorder in 1984. This 101 from NIMH explores the basics of the condition, from who develops it to how it is treated.

SAD uniquely affects people with attention-deficit hyperactivity disorder

Those with ADHD—chronic issues with attention and executive function—are primed for SAD. Many are disproportionately evening chronotypes (more awake in the evening), have a delayed sleep phase, and have low sensitivity to light in the morning. This podcast explores the overlap between these two groups.

One theory claims the retinae of SAD patients may fail to adjust to less light in winter

Most people’s eyes become more sensitive to light in the winter months, but some do not. This failure to adjust causes ripple effects on those individuals’ biological clocks. This Ted-ED video provides a clear, brief, narrative explanation of the condition in six minutes.

SAD disrupts melatonin secretion, producing it longer in the morning

The hormone is secreted from the pineal gland in the brain and is key to the timing of sleep. However, the substance does not generate sleep itself. With seasonal affective disorder, the body misperceives the photoperiod—the time with light—and the cycle of sleeping and waking gets off-phase, leading to issues with circadian rhythms.

Women are four times as likely to be diagnosed with seasonal depression

This prevalence trend mirrors the broader incidence of depression among women and is well-documented. Researchers suggest the disparity stems from differences in hormones, social role expectations, coping mechanisms, and more. Men may also present with depression differently, and seek help less.

Bupropion is the only antidepressant approved for the preventive treatment of SAD

Clinical trials showed a 44% reduction in risk for recurrence of SAD for those who took the drug compared to a placebo group. Bupropion is a norepinephrine–dopamine reuptake inhibitor, which increases dopamine (other common antidepressants, known as selective serotonin reuptake inhibitors, sometimes can suppress dopamine, but not always).

Norman Rosenthal’s struggle with SAD inspired him to understand it

The South African doctor migrated to New York City in the 1970s. During his first winter there, he noticed the shorter days had a significant impact on his mood compared to those in his hometown of Johannesburg, South Africa, which is much closer to the equator. After three years of this seasonal mood shift, he decided to focus his studies. Hear him speak in this quick narration.

Depression is much more than sadness—and isn't fleeting

The American Psychiatric Association's DSM-5—used for defining diagnoses—says a person must be experiencing five or more symptoms of depression most of the day over at least two weeks. Research indicates older people are less likely than younger people to meet that depression benchmark, though this article says they still often have at least several of the depression symptoms.

Key tips for helping the depressed—including listening without judgment

Major depressive disorder is a clinical diagnosis and is not a lifestyle choice. Those who struggle with depression can express persistent feelings that are difficult to process and make sense of for friends and family. This guide walks through some counterintuitive perspectives, including resisting the urge to force a depressed person to do the things that would make them feel better.

JJ Schildkraut theorized depression is linked to brain chemical imbalances—in 1965

Schildkraut was one of the first to put forward this idea, which stemmed from lab animal research. A decade later, researchers published the first landmark paper on fluoxetine—better known by trade name Prozac—which increases serotonin levels in the brain.

Bipolar disorder, which is characterized by extreme mood swings, affects nearly 3% of the US population

There are two types of this disorder. Bipolar 1 features a significant manic episode—abnormally elevated mood and frantic energy—followed by repeated depression, while Bipolar 2 vacillates between depressive episodes and hypomania, a milder form of mania, but not a full mania. Listen to this podcast as experts explain the condition.

Meteorological v. astronomical seasons, explained

Meteorologists and climatologists define seasons differently from “regular” or astronomical spring, summer, fall, and winter. Traditional seasons reflect the movement of celestial objects, known as the astronomical seasons; meteorologists mark seasonal change based on temperature averages.

Advent calendars have become a major seasonal driver for brands

Companies now treat Advent calendars as key holiday products, expanding production as demand surges across categories. Retail data shows beauty and self-care calendars consistently rank among the most popular, as some brands report selling out yearly, and retailers order months in advance.

The Sahm rule attempts to predict recessions based on unemployment trends

The US is in a recession when the average US unemployment rate over three months rises by half a percentage point from a 12-month low, according to the Sahm rule.

Schizophrenia symptoms often appear suddenly

Schizophrenia is a particularly shocking mental illness because its symptoms may appear seemingly without any prior signs of illness after a person has had no symptoms for the first couple of decades of their life. Among teens, symptoms may look like typical adolescent behaviors—withdrawal, being irritable, and having trouble sleeping.

Anticipatory grief describes experiencing sorrow ahead of a loss

All-consuming anticipatory grief—like if you know a loved one will soon die from a chronic illness—can be disabling. Seeking exercise, healthy food, hobbies, and trying to toggle between thinking about an upcoming loss and focusing on other matters is important for promoting health.

Stress is a response to external triggers, while anxiety is persistent and internal

When distinguishing the two, stress is a reaction to identifiable situations like deadlines or conflicts, and its symptoms fade when the stressor is gone. However, anxiety may jump from one worry to another over time without any apparent cause.

Genetic blood test offers an estimated clock on when Alzheimer's symptoms may appear

The 2026 research finding from researchers at Washington University School of Medicine in St. Louis—if validated in broader populations—suggests that an already available blood test could estimate when Alzheimer's symptoms may begin within a margin of several years. The test detects a protein called p-tau217 found in blood plasma and the researchers incorporated the findings from that blood test into a statistical model to come up with the symptom timeline predictions.

Pareidolia: the cognitive bias of finding meaning in randomness

Many people equate "random" with "well-spaced," creating a cognitive bias that influences how people interpret events. This article explains how people tend to assume a generative force behind the patterns produced by randomness. This phenomenon, known as pareidolia, is seen in claims ranging from backward messages hidden in reversed audio recordings to tea leaf readings.

A 'Simpsons' writer on the show's inadvertent predictions

Some have noted that "The Simpsons" has accurately anticipated a number of events years before they happened. In this interview, showrunner Al Jean explains how these unintentional predictions came about and why he believes the events were not so much visions of the future as educated guesses.

Read about the evolution of the S&P 500 and its recession recovery

Since the S&P 500 is considered a bellwether index (meaning it represents the health of the US economy), its value is important for investors in both bull and bear markets. The S&P 500 has been impacted by recessions and downturns, from the 1970s oil crisis to the dot-com crash of the early 2000s.

Avalanches happen when layered snow fails, often on perfect ski slopes

Snowpacks form unstable layers as weather shifts; a weak, refrozen layer buried under fresh snow can shear and release a slab avalanche on certain steep slopes. Triggers range from new snowfall to the movement of skiers, while survival depends on the presence of ski partners, beacons, and rescue teams.

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Explore an interactive map built from more than 100,000 survey responses on where people find joy in their lives

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

'Silent' fireworks have gained more interest in recent years as a quieter celebratory option.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Up to a million Girl Scouts sell about 200 million cookie boxes every spring, generating $800 million, largely because refusing a child is frowned upon

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

Sony set the standard for cylinder-shaped batteries when it repurposed manufacturing equipment used to make rolls of magnetic recording tape.

The 1987 Nintendo video game 'Stadium Events' isn't known for being particularly fun, but its scarcity has made it a highly sought-after item that has sold for up to $35K at auction.