MANILA, Philippines - Sexually transmitted diseases (STDs), generally, are quite easy to understand.

Among the most common infectious diseases that plague men and women in different parts of the world, STDs can be transferred from one person to another through, obviously, sexual contact -- vaginal and anal sex, oral sex, genital touching, and the use of "sex toys" such as vibrators.

Some of them are curable and not life-threatening. But if left untreated, some STDs may lead to cancer, pregnancy problems, and even death. (To know more about common STDs, click here.)

Despite the wealth of information available to the public (through doctors, books and the Internet), however, some people tend to believe in a number of myths about STDs.

US-based Centers for Disease Control and Prevention, for one, noted that one of the biggest STD myths is that "if you don't have symptoms, then you don't have an STD."

Eric Metcalf, MPH, an Indianapolis-based medical writer, editor and health educator, discussed 4 common myths about STDs.

His article, published on everydayhealth.com, was medically reviewed by internal medicine specialist Dr. Lindsey Marcelin, MD, MPH.

"Information is power. Get educated and keep yourself, and your loved ones, better protected with the facts," he said.

Below are the 4 myths, as mentioned in Metcalf's article:

You can always see signs of an STD

No, you can't instantly tell if someone is infected (or not) with an STD just by looking at their genitals, Metcalf said, citing sexual health educator Debra Herbenick, PhD.

"STDs are not usually visible at all. With genital warts, for example, people think you'll be able to see warts if you have them, or that you'll be able to see herpes if you have it," Herbenick said.

Metcalf stressed that even warts, which are commonly visible, cannot be seen by the naked eye.

Because of this, he said some people may infect others with STD without even realizing it.

Genital warts are caused by the human papilloma virus (HPV), and are usually characterized by rough, wart-like growths that may occur singly or in clusters. Lesions may also be present in the mouth or throat.

Since genital warts are very contagious, experts have advised patients to practice "safe sex." HPV vaccines are also available to prevent people from acquiring the said disease.

You can only catch herpes from a partner during an outbreak

One of the usual symptoms of genital herpes, an STD caused by the herpes simplex virus (HSV), is an outbreak of blister-like sores on the genitals which are contagious.

Even without the outbreaks, however, Herbenick said that partners of those with genital herpes can still get infected. According to her, people may get sores that are not even noticeable.

The presence of the HSV in a pregnant woman's birth canal may be dangerous to the infant -- the newborn child may acquire herpetic meningitis, herpetic viremia (herpes virus present in the blood) and chronic skin infection.

There is no known cure yet for genital herpes, but its symptoms may be reduced by oral or topical medications. To avoid the transmission of genital herpes, use condoms and don't share towels with others.

You can be tested for any kind of STD

Contrary to what most people believe, Metcalf said that testing is either limited or unavailable for some STDs.

For one, no test is available for HPV in men, and people can't be tested for bacteria called mycoplasma genitalium (which causes symptoms similar to chlamydia) in a clinic, he said, quoting Herbenick.

Chlamydia, one of the most common STDs, is usually treated with antibiotics but it's always best to consult a doctor before taking any medications.

You can catch HIV from casual contact

Until today, some people believe that people can get the human immunodeficiency virus (HIV) through casual contact such as kissing, hugging or shaking hands, Metcalf said. But this is not true.

Rather, he said that this spread between adults by sharing a body fluid such as blood either through sex or needles (during blood transfusions or from tattoo piercing).

HIV causes a condition called acquired immune deficiency syndrome (AIDS), which causes a person's immune system to fail. In other words, a person with AIDS may die from diseases that are generally harmless to healthy people.

There is no known cure yet for AIDS, but treatments that increase the quality of life of patients currently exist.