Our bodies are pretty good at flagging up if something’s not quite right. If you’ve eaten something off, you’ll no doubt soon find out. Step on a lego brick, your body will promptly alert you. Likewise, if you have a medical condition, then your body will often display a flurry of signs and symptoms.

However, there’s a fair few fascinating, relatively harmless, and surprisingly common medical conditions that can fall under the radar. As you'll see, many people with these biological quirks often view them as a blessing rather than a curse. 

Switcheroo Organs 

Approximately 1 in 10,000 people have their internal organs mirrored on the “wrong” side of their body, a congenital condition called Situs inversus. Their heart is on the right of their chest and their liver is on the left.

Despite this unusual mix-around, most people show no medical symptoms. In some cases, people are totally unaware of their condition (although you would think the heartbeat would give it away). Equally, many organs come in bilateral pairs – lungs, kidneys, eyes, etc, while others are central and singular, so you won't notice any change. Donny Osmond only became aware of his Situs inversus after suffering from appendicitis and doctors treating him realized the organ was not where they expected it to be. Enrique Iglesias and Catherine O’Hara also reportedly have Situs inversus.

Back in 2009, 53-year-old Jack Eigel became the first person with Situs inversus to undergo a heart transplant. He once joked: "You know, when I was little, I tried to pledge allegiance the wrong way and got a few teachers mad at me."

Tasting Words

Smelling musical riffs, tasting words on a map, feeling a sense of color when someone yawns. This might sound extraordinary, but it is perfectly ordinary to a surprising number of people – this is just how the world is perceived by them.

Synesthesia is a neurological condition where the senses entangle and one stimulation of a sense involuntarily sparks the stimulation of another. For example, people with synesthesia commonly often associate certain words or numbers with a particular color. A recent study argued that up to 20 percent of the population could experience some degree of synesthesia, however, a more conservative estimated is 2 to 4 percent.

As you can imagine, synesthesia can open the doors of perception to some incredible things. Many renowned musical and visual artists claim (although very few have had it verified) to have synesthesia and say it helps with the artistic process, including Pharrell Williams, Billy Joel, Kanye West, Hans Zimmer, and David Hockney, 

The Women With Super Vision

We see color thanks to different types of cone cells, photoreceptor cells in the retina of eyes that all pick up on different wavelengths of light. Most people have three different types of cone cell, yet approximately 12 percent of women might have four distinct cones, a condition called tetrachromacy.

But why mainly females?

Females have two X chromosomes, while males have an X and Y chromosome. The genes responsible for red and green cone cells are located on the X-chromosome. To have tetrachromacy, you need two copies of these genes from the X chromosome. By no coincidence, that’s also why men are more likely to be colorblind than women because they only have “one shot” at having the full gene.

Most people see tetrachromacy as a positive attribute because as they anecdotally say, it allows them to have a subtler and more sensitive sense of color. However, don’t be fooled by viral online tests claiming they can identify whether you have tetrachromacy – they don’t work.

Aphantasia 

You’ve probably never even heard of it, however, it’s thought one in fifty people might have a condition called aphantasia.

People with aphantasia, a condition that has only just been formally recognized, find it hard or impossible to create a mental image. If you were to ask some with aphantasia to imagine, for example, the image of a dog with an apple on its head, they wouldn’t be able to do so. Like most mental conditions, it appears to exist on a spectrum. Some people have it so severely they are even unable to imagine the faces of loved ones, yet they are able to recognize them perfectly when they see them.

Adam Zeman, a professor of cognitive and behavioural neurology who coined the phrase aphantasia, told BBC News in 2015: “People who have contacted us say they are really delighted that this has been recognised and has been given a name, because they have been trying to explain to people for years that there is this oddity that they find hard to convey to others."

Joint Hypermobility

Everyone has a friend with an endearingly freakish ability to put their leg behind their head or twist their arm in an eye-watering way. In most instances, these people have been simply training their joints to do this through practice (knowingly or unknowingly) and just say they are “double jointed”.

However, there is a chance they have joint hypermobility syndrome, a condition that means your joints are more flexible than the general population, but you also experience other symptoms like joint pain, a tendency to sprain joints, poor balance, slightly stretchy skin, and digestive problems. It’s believed that only one in 20 people with the condition are given the correct diagnosis. Underlying causes can vary, but it tends to be genetic, resulting from a variation in levels of collagen, the main structural protein of connective tissue.

Here’s where it gets extra interesting. A few studies have found that people with hypermobile joints also have heightened activity in brain regions associated with anxiety and the “fight or flight" response. Scientists still can’t agree why.

Last, But Not Least: Herpes

We hate to break it to you, but you probably have herpes.

A World Health Organisation (WHO) study from 2015 estimated that over 3.7 billion people, around two-thirds of the world population under 50, are infected with a strain of the herpes simplex virus (HSV). The vast, vast majority of people are infected with HSV-1, the strain of the virus that causes cold sores. Around 417 million people aged 15 to 49 (11 percent) worldwide have a HSV-2 infection, the strain that can cause genital herpes.

As you might have guessed, only a few people exhibit any clear symptoms, while the majority will the infected will go around totally unaware.