Summer, sadly, doesn’t last forever. Soon we’ll be wondering where all the light has gone. Then some of us will feel the onset of seasonal affective disorder (SAD), the condition that gives people depressed moods every fall and winter. SAD is no laughing matter—it can make a big chunk of the year a terrible time for sufferers and can hurt their relationships, job performance and overall health.

That’s why Bottom Line Personal keeps up with every development that can help our readers with SAD and why we recently caught up with Georgetown University’s Norman E. Rosenthal, MD, a pioneer in the field of SAD research, to get the latest facts about SAD and how to treat it. What he told us…

Not everyone who gets SAD in the fall and/or winter feels sad. Depression is the best-known symptom of SAD, but people who have relatively mild SAD may not become depressed. As a result, they might fail to realize that they have SAD and never seek treatment. But even mild cases can have serious ­consequences. Mild SAD can produce a decline in energy and productivity and an increase in appetite (especially for carbohydrate-rich foods), easily resulting in unhealthful weight gain.

What to do: If your energy levels are consistently down or your appetite up during times of year when you do not get much sunlight, you might have SAD—so try a do-it-yourself SAD treatment for a few weeks and see if these symptoms fade. To do this, get outside in sunlight for 30 to 60 minutes each day, even if you must bundle up against cold temperatures to do so…or use a light-­therapy lamp for 30 to 60 minutes each day. (More on light-therapy lamps and other SAD treatments below.) Try to get your light (whether from the sun or a light-therapy lamp) in the mornings—that’s when research suggests light is most effective at staving off SAD.

Size matters if you buy a light-­therapy lamp. You can find light-­therapy lamps online and in stores for as little as $30, and almost all of them claim to produce the 10,000-lux light intensity that’s recommended and effective for treating SAD. What the lower-end lamp makers tend not to mention is that their lamps might deliver 10,000 lux only if you position your eyes an inch or two from the light, which is impractical and uncomfortable.

What to do: Select a light-therapy lamp that produces 10,000 lux from a lit surface that measures at least 12 ­inches by 18 inches. Light-therapy lamps this size tend to remain effective over a significantly longer distance. Examples: Carex Day-Light Classic Bright Light Therapy Lamp, 10,000 lux up to 12 inches away (Carex.com, recently about $115 at Amazon.com)…Sunbox SunRay II, 10,000 lux up to 23 inches away ($359 at Sunbox.com).

Fall/winter SAD treatments need not increase skin cancer risks. It turns out that it isn’t the sunlight that reaches our skin that wards off SAD. It’s the sunlight that reaches our eyes. When the eyes receive bright light, it triggers the release of mood-regulating neurotransmitters such as serotonin that seem to combat SAD. That means you can apply sunscreen to keep your skin safe when you head outside without increasing your risk for SAD. It also means that you can successfully treat SAD with a light-therapy lamp that filters out potentially dangerous UV rays, as most do. (Though for other health reasons, it’s good to let some sun reach your skin—see below.)

Caution: Do wear sunglasses outside on bright days if you are not trying to treat SAD…or when you spend more than an hour in bright sunlight during a day. Excessive amounts of bright light can increase cataract risk.

Exercise and mind-set can help treat winter SAD, too. Light therapy is the best-known treatment for SAD, but if light alone doesn’t do the trick, there are other treatments you can try. Exercising causes the body to release SAD-combating neurotransmitters such as serotonin just as bright light does. And a professor at University of Vermont has shown that cognitive behavioral therapy, a form of talk therapy that modifies negative thoughts, can be helpful, too.

What to do: Don’t just go outside for 30 to 60 minutes of sunlight in the winter—exercise outside for at least part of this time. If you struggle to drag yourself out of bed in the morning for exercise and sunshine, make plans with a friend or personal trainer to exercise together. Adding another person increases the odds that you will follow through.

When you catch yourself engaging in negative self-talk in the fall/winter, counter with positive responses. Example: You think, I’m so lazy. Immediately question this by reviewing things that you have done that weren’t lazy…and then think, Let’s see what I can do today.

If none of this cures your SAD, ask your doctor about cognitive behavioral therapy with a qualified therapist and about pharmaceutical treatments or supplements—prescription antidepressants can be effective for SAD.

There is a summer version of SAD, but it isn’t like its winter cousin. Winter SAD typically brings depressed moods, low energy and an increase in appetite…but there’s also a summer version of this condition. Summer SAD, also called reverse SAD, generally produces agitated moods, insomnia, loss of appetite and, in some cases, suicidal ideas. This might explain why there are more suicides in the summer than in the winter in the US, even though winter is the time of year that most people tend to associate with bleak moods. Another difference—while winter SAD is caused by insufficient exposure to sunlight, the cause of summer SAD is less clear-cut. It could be too much sunlight…hot temperatures…or some combination of the two.

What to do: If you regularly experience agitation, insomnia, decreased appetite and/or suicidal thoughts during weeks when you spend lots of time in the summer sun or in hot weather, cut back on time in bright sunlight…take cool showers, baths or swims midday…turn up the air-conditioning…make sure that your bedroom is very dark when you go to bed and until you wake up—add blackout shades/curtains if necessary. If symptoms persist, discuss what you are experiencing with a medical doctor or therapist.