Why is there always a need for new medicines and why are new illnesses always developing?

I strongly believe that it is because of the increasing number of toxins around us, the food that we eat (people live to eat, not eat to live) lifestyles, etc.

People who don't finish antibiotics can become sicker and develop more intense infections. They can also become resistant to antibiotics because of this, drug companies are getting rich developing new and improved medications for people who are resistant to the current drugs in use. Another factor is people who don't wash their hands after treating someone especially in hospitals. They may go from one patient to the next spreading infections, this is usually how MRSA is acquired. Each person's immune system reacts a little different to antibiotics, where one person gets well with a treatment another person may recover only slightly and need a stronger course of medication to treat the same infection.

In many cases illnesses are a virus. As they are a living particle and they have been threaten in different ways they try to develop and become little by little more immune to the usual vaccine. as you said also environmental changes help them since environment can make them stronger or change them in some chemical way that it cannot be manage the same way that it was before.

Many diseases start out as animal diseases and mutate to become human diseases. Then they further mutate to have the capacity to spread among the human population. As for the medicines, I'm guessing as they mutate they may become indifferent to any previous medicine that had worked.

Mutation? Viruses becoming resistant to current medicines?

WEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEINERRRRRRRRR.