Why does the body develop a stronger and faster response to a pathogen upon reinfection?

When you first meet a pathogen, your immune system learns to recognize it and creates special cells called memory B and T cells that remember its shape. These memory cells stay in the body long after the first infection. If the same pathogen comes back, the memory cells quickly find it and jump into action, producing antibodies and killing infected cells much faster than during the first encounter. This rapid, focused response is why the second infection is usually milder and clears up sooner. For example, if you get chickenpox once, your body remembers the virus, so a second exposure—like a smallpox vaccine—eliminates it almost instantly.