Now is the summer of our contentment, with winter a distant memory and autumn a comfortably long way off. But don't be fooled by the lure of vacation time and daydreams of weekend barbecues -- summer is fraught with danger.

Brain Freeze

If you've just scarfed down a sundae too quickly, you may be suffering from sphenopalatine ganglion neuralgia. That mouthful of Greek and Latin is the scientific term for ice cream headache or brain freeze, where you're assailed by stabbing head pains after attacking your double chocolate-chip scoop.

Scientists still aren't quite sure just how cold things in the mouth cause ice cream headache, but it's thought that cold food or drink might stem from the rapid cooling and rewarming of tiny blood vessels in the sinuses, which causes them to constrict and dilate quickly. That movement could be sensed by pain receptors and sent to the brain through a major conduit called the trigeminal nerve. Since the nerve primarily senses pain in the face, the brain thinks the pain from the sudden cold is from the forehead.

Another possible explanation is that the cold sensation causes the anterior cerebral artery to automatically dilate, increasing blood flow to ensure that the brain stays warm. The sudden influx of blood causes pain by increasing pressure inside the brain. Harvard Medical School researchers offered this explanation, based on brain imaging of 13 volunteers sipping ice water, at the Experimental Biology 2012 meeting on April 22 in San Diego, as noted by LiveScience. That study has not yet been published in a peer-reviewed journal.

Pretty much anyone can get a brain freeze, but people who are prone to migraines or have a history of head injuries may be especially susceptible to ice cream headaches, according to the Mayo Clinic.

Roller Coasters

The specter of death is part of roller coasters' seductive appeal -- the dopamine rush from the simulated danger of a loop-the-loop or a stomach-lurching drop is like a natural drug. Sometimes, however, mechanical failure or idiotic behavior can result in very real tragedies.

In 2005, U.S. Centers for Disease Control and Prevention, or CDC, researchers published a paper examining roller coaster-related deaths that occurred between 1994 and 2004 in the journal Injury Prevention. They found that, during this period, 40 people were killed in 39 separate incidents on roller coasters -- 29 amusement-park guests and 11 employees.

Twenty-two of the fatalities resulted from external causes: falling from a roller coaster, being struck by a passenger in a roller coaster, or abdominal trauma after the roller coaster suddenly stopped. The other 18 fatalities examined by the study stemmed from medical conditions either caused by or worsened by riding in a roller coaster -- eight cases of bleeding in the brain, eight heart or artery conditions, one asthma attack, and one unknown condition.

Still, roller coasters account for an average of just four deaths a year in the U.S., the researchers noted.

It's hard to pin down exact statistics on accidents and injuries directly related to roller coasters -- the Consumer Product Safety Commission, or CPSC, a federal agency, lumps roller coasters in with a host of other kinds of amusement-park rides, including mechanical bulls, ball pits, and carousels.

Numbers from the amusement-park industry show that the rate of injury related to fixed-site rides at amusement parks is fairly low -- a little less than five injuries per 1 million patrons, according to a report prepared by the research group National Safety Council for the International Association of Amusement Parks and Attractions.

However, one roller coaster is designed to kill people. While studying for his doctorate in design interactions at London's Royal College of Art, Julijonas Urbonas drew up plans for an attraction that would give suicidal folks the best, last ride of their lives.

Urbonas' hypothetical Euthanasia Coaster would begin with a 1,600-foot climb, followed by a precipitous descent through seven huge loops that would spin the riders so fast and so hard that their brains wouldn't get enough oxygen to keep functioning.

In a video, the deadly ride's designer described his creation as engineered to humanely -- with elegance and euphoria -- take the life of a human being.

Slipping, Sliding, Crashing

Waterslides are kind of like roller coasters if you take away all the safety restraints, so it's no surprise that they account for their fair share of accidents -- more than any other kind of amusement-park ride.

The CPSC's National Electronic Injury Surveillance Survey estimates that between 1998 and 2007, about 3,819 people sought treatment for injuries sustained at water parks. During the same period, there were 3,344 injuries on roller coasters and flume rides, according to the survey.

Going down headfirst on a waterslide is much riskier than going feet first. In a 2008 report in the Clinical Journal of Sport Medicine, Turkish researchers described how four men were hurt when their heads hit the floor of a shallow splashdown pool at the end of the slide, resulting in broken vertebrae, slipped discs, and nerve damage.

All the men required surgery, one lost motion in his arms and another lost the ability to move all of his limbs after the injuries.

If you decide that water parks are too dangerous and think you can enjoy a waterslide in the safety of your own backyard, you may want to think again. Slip-N-Slide style products, with a sheet of plastic designed to be hooked up to a garden hose, aren't meant for use by adults or teenagers, according to the CPSC.

Because of their weight and height, adults and teenagers who dive onto the waterslide may hit and abruptly stop in such a way that could cause permanent spinal cord injury, resulting in quadriplegia or paraplegia, the CPSC said in 1993.

Drowning Pool

But the most dangerous summertime setting isn't the water park or a death-defying roller coaster -- it can be as small as a backyard pool.

The CDC places drowning fifth on the list of causes of unintentional injury-related death in the U.S., and estimates that about 10 people die each day from unintentional drowning. Of those 10, two are children under 14. For each child who drowns, five others have to go to the emergency room for nonfatal injuries.

The two groups most at risk of drowning are males of all ages and races, and African-American children, for whom the drowning rate is almost three times the rate of white children in the same age range. The CDC says one major reason for this racial  disparity is probably a lack of access to pools in minority communities, which contributes to a lack of familiarity with aquatic activity and lower rates of swimming competence.

Little Lake Monsters

Even if you're a decent swimmer, you can still find things to be afraid of in the water. Tiny things.

The freshwater amoeba Naegleria fowleri is known to invade human nervous systems through the nose. The microscopic creature crawls up to the brain via nerve fibers and begins chowing down on its victim's gray matter and causing a catastrophic infection that spreads throughout the entire central nervous system.

The death rate is extraordinarily high at about 97 percent. Patients usually die within two weeks as the amoeba-induced infection consumes the medulla oblongata, cutting off the person's ability to breathe.

Naegleria fowleri killed  33 people between 1998 and 2007, according to the CDC. A spate of several cases last year drew media attention, particularly when three people died last August. It's known to have infected people swimming in lakes, but people have also caught it by flushing their sinuses with tap water using neti pots.

Walking On Sunshine, And It Doesn't Feel Good

The wary vacationer may just decide to forgo all sorts of activity that involves moving parts or water and settle for reading the latest inexplicably popular shlock novel while sunbathing.

But the wary vacationer shouldn't get too engrossed in turning the pages of his or her paperback and forget to reapply his or her sunscreen, lest the wary vacationer get sunburned and raise his or her risk for skin cancer.

Different kinds of sun exposure are associated with different kinds of skin cancer, according to the CDC: Outdoor workers who experience continuous sun exposure are more likely to get squamous cell carcinoma, while the occasional sunbather is more likely to get melanoma and basal cell carcinoma. Though it is comparatively less common, melanoma is the deadliest form of skin cancer.

Health officials say the best way to avoid sunburn is to encourage people -- especially young people -- to take protective measures like wearing sunscreen or broad-brimmed hats, and to provide shade in public areas.

In 2010, the CDC and the National Cancer Institute surveyed nearly 5,000 adults and compared their efforts to protect against sunburn to those reported in similar surveys in 2000 and 2005. They reported their results in May.

They found that while young adults in 2010 took a bit more caution in the sun than their peers had in previous years -- by wearing sunscreen or long clothing -- one-half of those surveyed had had at least one sunburn in the past year. White people were the most likely to get at least one sunburn, with nearly two-thirds reporting a burn in the past 12 months.

Now go out and enjoy your summer break!