Sexually transmitted infections (STIs) are a big public health issue, affecting millions of people around the world every year. It’s important for anyone who is sexually active, or thinking about becoming sexually active, to understand how STIs are spread. This knowledge helps people protect themselves and make smart choices about their health. In the US, STIs like chlamydia, gonorrhea, and genital herpes are common, especially among teenagers and young adults. Even though there have been improvements in testing and treatment, the number of cases is still rising. This shows why it’s so important to know how STIs are caught and how to prevent them.

Chlamydia is a very common sexually transmitted infection (STI). It is a bacterium that can spread in semen or vaginal fluid and infect the vagina, uterus (womb), urethra (tube for the passage of urine, plus semen in men), the penis, rectum and, less commonly, the throat and eyes. It may cause no symptoms at all but if it does, signs to look out for are a vaginal, penile or rectal discharge. This is usually watery and white or cloudy, and there may also be pain or stinging when peeing. In the longer term, men may get pain in the testicles and women develop pain in the pelvis, especially when having sex, and bleeding after sex or between periods. Ultimately it can cause infertility if left untreated. It may also cause joint inflammation (arthritis) and irritated red eyes (conjunctivitis). Given the high stakes and the fact that you may have no symptoms at all, it’s important to get tested regularly. This is especially important if you are aged 16 to 25, as this is the highest risk age group. If you're a woman, sexually active and under 25, it's recommended that you have a chlamydia test once a year, and when you have sex with new or casual partners. If you're a man, sexually active and under 25 it's recommended that you have a chlamydia test once a year if you’re not using condoms with new or casual partners. Get an STI test at the change of any partner (use condoms until you both get the all-clear) and if you’re changing partners regularly or have multiple partners, get tested every three months.

Erectile dysfunction is when you are unable to get an erection or maintain an erection in order to have sex. It can sometimes be referred to as impotence or shortened to ED, and it is a very common symptom men can experience from time to time. In most cases, there is no serious underlying cause, and it may improve on its own, although it is important to know there is a treatment that can help. It is especially common in older men, with around 1 in 2 men over the age of 40 experiencing ED at some point. Some of the things that can contribute to erectile dysfunction include tiredness, stress, or excessive alcohol. The causes of longer-term erectile dysfunction can be split into 3 main types, which are psychological, physical health, and medication-induced. Psychological causes of erectile dysfunction include stress, performance anxiety (or any anxiety around having sex), relationship issues, or mental health conditions such as depression. With psychological causes, erectile dysfunction usually starts suddenly, not gradually, and it is best to treat the cause (e.g., the mood symptoms) rather than treating the symptom of erectile dysfunction. Treat the mood symptoms, and the erectile dysfunction will hopefully improve. Physical causes are usually the reason for ED in men over 40, with reduced blood flow to the penis being at the top of that list. The arteries in the penis become too narrow for enough blood flow to cause an erection. Men who smoke, have high blood pressure, or have high cholesterol levels are more at risk of developing this. With physical causes, erectile dysfunction tends to occur more gradually over time rather than suddenly. Chronic health conditions that affect nerves or blood flow, such as diabetes or multiple sclerosis, can also cause ED, as well as any damage to the penis or low testosterone levels, however these are less common. Some medications can cause or make erectile dysfunction worse. These include some of the medications used to treat depression, high blood pressure, and prostate problems. It is best to discuss this with your doctor if you think this might be the case. Don't stop taking the medication before speaking with your doctor.

The cervix is known as the neck of the womb and is a narrow muscular opening connecting the vagina to the womb (uterus). Cancer can affect any part of the cervix. Cervical cancer is most commonly caused by certain strains of a virus called the Human Papilloma Virus (HPV). The risk of cervical cancer has been much reduced with both the US’s cervical screening program and the HPV vaccination program. It's a relatively uncommon cancer but receives a lot of attention as it is so easily prevented if early cell changes are caught and because it affects young women who are otherwise healthy and at low risk of other cancers.

Warts are small fleshy growths or bumps with a hardened dry top, most often flesh-colored, but can appear red if irritated. Several can appear in a cluster. Genital warts are sexually transmitted infections caused by the human papillomavirus (HPV) and spread by vaginal, anal, digital, and oral sex or sharing sex toys. They are not harmful and can disappear within a few months, but they can become irritated and sore if they rub or catch on clothing, and some people are bothered by their appearance. You also put your partner or partners at risk of contracting them if left untreated. Depending on their size or location, they may catch on clothes or feel a bit sore and sometimes itch or bleed. They may not cause you any bother. Or you may be bothered by your appearance, which can affect your confidence and, inevitably, intimate relationships.

Gonorrhea is a common sexually transmitted infection (STI) caused by a bacteria called Neisseria gonorrhoeae. This can easily pass from person to person via unprotected vaginal, anal, and oral sex or sharing of sex toys. Condoms help to prevent catching gonorrhea. This may cause no noticeable symptoms, or it can cause a yellow/green, watery, or pus-like discharge from the penis, vagina, or rectum. It may cause pain on peeing; for women, pain during sex, bleeding after sex, or bleeding between periods, and for men, pain in the testicles. It can cause joint inflammation (reactive arthritis) and eye symptoms (conjunctivitis) and, if left untreated, can cause infertility. Given the high stakes and the fact that you may have no symptoms, it’s important to get tested regularly. This is especially important if you are 16 to 25, as this is the highest-risk age group. Get an STI test at the change of any partner (use condoms until you both get the all-clear) and at least once a year.

Oral herpes, also known as cold sores, are small blisters on the face that are caused by the herpes simplex virus (HSV). These blisters pop and then get a crust over them. Some people experience tingling or burning before the blister appears, which can be painful. They are very common, with around 1 in 5 people suffering from repeated cold sores. They usually heal by themselves between a week and 10 days. Most people are infected with the virus when they are young. However, they may not get a cold sore until many years later. Once infected, the virus stays within you and can be reactivated and cause other cold sores at future points. This is usually around times of stress, tiredness, menstruation, illness, or some people find the sun can cause outbreaks. Genital herpes and cold sores are caused by the same virus, although there are two different strains (HSV1 and HSV2). It isn’t really important which one is causing trouble, as treatment is based on where your symptoms are happening. If you have the symptoms below, see your sexual health doctor to discuss them.

Genital herpes is a common infection caused by the herpes simplex virus (HSV) that also causes cold sores around the mouth. Herpes is spread through skin-to-skin contact, including vaginal sex, anal sex, and, occasionally, oral sex. It causes painful blisters on the genitals and the surrounding areas, usually preceded by a tingling sensation. It is most sore the first time you have it. As with many viruses, they can't be eradicated from your system, but symptoms and outbreaks are treatable. See your doctor as soon as possible for confirmation and treatment.

Herpes is a viral infection caused by the herpes simplex virus. There are two common places the herpes virus can be found, near the mouth (oral herpes), which is also commonly known as a cold sore, and around the genitals (genital herpes). A herpes infection typically starts with a change in sensation - pain or tingling in a particular area - followed by small blisters that burst and leave small painful ulcers. If they are near the vagina, they can cause nasty pain when going to the bathroom. There are two forms of the herpes simplex virus, types 1 and 2. Type 1 is more commonly associated with oral herpes, and type 2 is more commonly associated with genital herpes. Although due to the fact the condition spreads via contact, and aided by oral sex, it is not uncommon to find either type in any location. There is no way to distinguish from symptoms. They present in the same way and require a test to see which type is causing trouble (although the type doesn't change anything clinically - treatment is given depending on where it is infected). Oral herpes is commonly acquired in childhood and passed on via skin-to-skin contact, or via contact with fluid in the blisters from the area of infection. Genital herpes is also spread through skin-to-skin contact, including vaginal sex, anal sex, and oral sex.

Lichen sclerosus is a skin condition in which you might notice the area feels tight or itchy. It may be painful when passing urine, having sex, or – for men – getting an erection. If it's around the anus, you may find it sore when passing a stool. Skin can become fragile and bleed if rubbed or scratched and then feel very sore if it breaks down. It may form blood blisters or thickened areas with constant scratching. At first, there may be nothing to see on the skin. Later in the process, you may notice shiny white patches where it feels sore or itchy.