Hepatitis C is caused by the hepatitis C virus (HCV), a blood-borne pathogen that infects liver cells. The virus spreads almost exclusively through direct contact with infected blood, and an estimated 50 million people worldwide are living with chronic infection, with roughly 1 million new cases each year.
The Virus and How It Attacks the Liver
HCV is an RNA virus in the same family as dengue and Zika. Once it enters your bloodstream, it targets hepatocytes, the primary working cells of the liver. The virus latches onto receptors on the surface of these cells, gets pulled inside, and hijacks the cell’s machinery to copy itself. New viral particles are then released into the blood, where they infect more liver cells.
What makes HCV especially persistent is its ability to disarm your immune system early on. Certain viral proteins block the signaling pathways your body uses to detect and fight infections. One set of proteins interferes with the system that recognizes foreign genetic material inside cells. Another inhibits a key antiviral defense that your immune system activates in response to viral threats. The result: your body mounts an immune response, but in most cases it’s not strong enough to clear the virus. Even people who do clear it naturally aren’t protected from getting infected again.
Injection Drug Use Is the Leading Cause
Sharing needles, syringes, or any equipment used to prepare or inject drugs is the single most common way HCV spreads. Even a tiny amount of dried blood on a syringe or cooker can carry enough virus to cause infection. This doesn’t require visible blood. Microscopic traces are sufficient.
This remains the primary driver of new infections in many countries. Any situation where blood from one person can enter the bloodstream of another through a puncture wound creates a potential route for the virus.
Blood Transfusions and Organ Transplants
Before 1990, receiving a blood transfusion was a significant risk factor. HCV was discovered in 1989, and antibody screening of donated blood began the following year. That single change transformed the safety of the blood supply. The current risk of getting HCV from a screened blood transfusion in the United States is roughly 1 in a million per unit transfused.
In countries with well-established screening programs, this route of transmission is now extremely rare. However, in parts of the world where blood screening infrastructure is limited, transfusions and medical procedures using unsterilized equipment continue to contribute to new infections. The Eastern Mediterranean region carries the highest burden globally, with 12 million people chronically infected.
Tattoos, Piercings, and Unsterile Equipment
Getting a tattoo or piercing in an unregulated setting is a recognized, though less common, route of transmission. The risk comes from needles, ink, or tools that have been contaminated with someone else’s blood. Licensed, reputable studios that use single-use needles and sterilize equipment between clients pose very little risk.
If you’re getting body art, watch for a few things: needles and ink should be opened from sealed packaging in front of you, the work area should be visibly clean, and the artist should wear fresh gloves. The same principle applies to any setting where skin is pierced, including acupuncture or informal medical procedures in under-resourced areas.
Mother-to-Child Transmission
A pregnant person with active HCV infection can pass the virus to their baby during pregnancy or delivery. This happens in about 6 to 7 percent of exposed pregnancies. The risk roughly doubles, to around 12 percent, if the mother also has poorly controlled HIV.
Several factors appear to increase the likelihood of transmission during birth. Prolonged rupture of membranes (six hours or more before delivery) and the use of internal fetal monitoring have both been associated with higher risk. Having detectable virus in the blood is a prerequisite for transmission, but researchers haven’t identified a specific viral load threshold that makes it more or less likely.
Sexual Transmission
HCV can spread through sexual contact, but this is uncommon compared to other routes. The virus is not as easily transmitted sexually as hepatitis B or HIV. However, certain factors raise the risk: having multiple sexual partners, having an existing sexually transmitted infection, being co-infected with HIV, and engaging in anal sex. These factors likely increase risk because they involve a greater chance of blood-to-blood contact through small tears or abrasions in tissue.
For people in long-term monogamous relationships where one partner has HCV, the transmission rate through sex alone is very low.
Other Less Common Routes
A few additional scenarios can lead to HCV transmission, all tied to the same principle of infected blood reaching another person’s bloodstream. Sharing personal items like razors or toothbrushes with someone who has HCV carries a small risk, since these items can have trace amounts of blood on them. Healthcare workers face occupational exposure through needlestick injuries, though the risk from a single needlestick involving an HCV-positive source is relatively low.
How HCV Does Not Spread
Because HCV is strictly blood-borne, many everyday forms of contact pose zero risk. You cannot get hepatitis C from hugging, kissing, holding hands, coughing, or sneezing. Sharing food, eating utensils, or drinking glasses does not transmit the virus. It does not spread through water or through breastfeeding. Casual household contact with someone who has HCV is safe, as long as items that could carry blood (razors, nail clippers) are not shared.
Why Most Infections Become Chronic
After exposure, the virus typically incubates for several weeks before any signs appear, and most people with acute infection have no symptoms at all. This silent early phase is one reason the virus spreads so effectively: people don’t know they’re infected.
The bigger issue is what happens next. In roughly 70 to 80 percent of people who contract HCV, the immune system fails to eliminate the virus completely. The infection becomes chronic, meaning the virus continues replicating in the liver indefinitely. Over years or decades, this ongoing infection can cause progressive liver damage, scarring (fibrosis), and eventually cirrhosis. The virus’s ability to suppress early immune defenses, combined with its rapid mutation rate, makes it difficult for the body to catch up once the infection takes hold.
Modern antiviral treatments can now cure more than 95 percent of chronic infections, but millions of people worldwide remain undiagnosed and untreated, largely because the virus can persist for years without obvious symptoms.