Why Do Some People (Especially Red Heads) Have Freckles?

iStock.com/NinaMalyna
iStock.com/NinaMalyna

For some people, freckles are a cosmetic obstacle. For others, they're a hot fashion accessory. But what causes the skin sprinkles that some people call "angel's kisses"? Basically, it's all in your genes—and the sun.

Freckles are concentrated flecks of melanin, a pigment protein. Melanin shows up when ultraviolet radiation (UV) hits the skin. UV is damaging, and melanin protects the skin from that damage by darkening it—think of it like your skin slipping on a pair of shades.

Melanin is produced in a type of cell called melanocytes. In some people, melanocytes are spread out evenly, and sun exposure produces a smooth wash of melanin, also known as a tan. In others, melanocytes are bunched up, and the sun produces crazy constellations of melanin, a.k.a. freckles. 

So why do redheads tend to have more freckles? Because both red hair and freckles are usually caused by the same gene, MC1R. The gene perches on melanocytes and controls the pigment balance in both hair and skin. When MC1R is working the way it normally does, it converts any pigment the body produces into eumelanin, which is responsible for black and brown hair and skin colors. When the MC1R gene is “broken,” it allows a rarer type of human pigment, pheomelanin, to build up in the body. Pheomelanin causes reddish hair and the rusty look of most freckles. Variations of the MC1R may also control the number of freckles people have.

But MC1R isn’t the only gene causing freckles. About a decade ago, scientists discovered another gene responsible for freckles in Chinese populations. Other genes may be involved too—scientists have yet to unravel all of the genetic causes behind freckles, which occur in a variety of ethnic groups. Regardless of the precise genetic mechanism, freckles are always a family affair: Parents pass on the likelihood of freckling, as well as its locations across the body.

While some pigmented skin disorders can also cause freckling, freckles by themselves are not a cause for concern (unlike moles, which are raised bumps on the skin—freckles are flat). But if you have freckles, make sure to wear plenty of sunscreen, since the areas where the freckles aren’t located will be especially susceptible to sunburn. You can think of them as spelling out your own little reminder system.

Why Does Hand Sanitizer Have an Expiration Date?

Hand sanitizer does expire. Here's why.
Hand sanitizer does expire. Here's why.
galitskaya/iStock via Getty Images

The coronavirus pandemic has turned hand sanitizer from something that was once idly tossed into cars and drawers into a bit of a national obsession. Shortages persist, and people are trying to make their own, often to little avail. (DIY sanitizer may not be sterile or contain the proper concentration of ingredients.)

If you do manage to get your hands on a bottle of Purell or other name-brand sanitizer, you may notice it typically has an expiration date. Can it really go “bad” and be rendered less effective?

The short answer: yes. Hand sanitizer is typically made up of at least 60 percent alcohol, which is enough to provide germicidal benefit when applied to your hands. According to Insider, that crucial percentage of alcohol can be affected over time once it begins to evaporate after the bottle has been opened. As the volume is reduced, so is the effectiveness of the solution.

Though there’s no hard rule on how long it takes a bottle of sanitizer to lose alcohol content, manufacturers usually set the expiration date three years from the time of production. (Because the product is regulated by the Food and Drug Administration, it has to have an expiration date.)

Let's assume you’ve found a bottle of old and forgotten sanitizer in your house somewhere. It expired in 2018. Should you still use it? It’s not ideal, but if you have no other options, even a reduced amount of alcohol will still have some germ-fighting effectiveness. If it’s never been opened, you’re in better shape, as more of the alcohol will have remained.

Remember that sanitizer of any potency is best left to times when soap and water isn’t available. Consider it a bridge until you’re able to get your hands under a faucet. There’s no substitution for a good scrub.

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Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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