Why don't pills work to cure allergies and asthma? Because they don't address the root cause. When the normal avenues for the body's waste removal became blocked, secondary routes must be employed. If the colon is blocked, the body will get rid of wastes through the skin or the lungs. It's survival. Classical experts called this Vicarious Elimination - the emergency exit.
Excerpted from Journey to the Center of Your Colon at. thedoctorwithin.com
VICARIOUS ELIMINATION – ASTHMA, ALLERGIES, DIABETES, ACNE …
A classical principle of traditional nutrition science, Vicarious Elimination is the term coined by JH Tilden, MD a century ago. Never has it been more accurate and relevant than it is today, with Americans fatter sicker and dumber than ever before.
Excerpt from the Enzymes chapter:
TOXEMIA AND VICARIOUS ELIMINATION
Toxemia means blood poisoning. Way back in 1926, a famous Colorado healer, JH Tilden MD, wrote a book which was the culmination of a lifetime of clinical experience, Toxemia Explained. Dr. Tilden was radical. He didn’t believe drugs cured disease. He had one simple thesis:
“… every so-called disease is a crisis of toxemia, which means that toxin has accumulated in the blood above the toleration point. … the crisis, the so-called disease – call it cold, flu, pneumonia, headache, or typhoid fever – is a vicarious elimination. Nature is endeavoring to rid the body of toxin.” Toxemia Explained p. 49 
A disease is named for where the toxins accumulate so much that that body part starts failing.
This model of disease, known as vicarious elimination, has never been disproven.
What happens is, the normal avenues for expelling waste – liver, kidneys, and colon – are overwhelmed. As a survival instinct, other organs of the body become enlisted to help get rid of wastes. They try desperately to expel the indigestible, rotting poisons, often becoming inflamed or diseased themselves in the attempt.
One obvious example of this idea is acne. Acne is not a skin problem. It is a vicarious elimination: the blood and the colon are so backed up with poisons that are accumulating faster than they can escape that the body tries an extreme solution: expel the poisons through the body’s largest organ: the skin. An alternative escape route. As the poisons leave, they irritate the normal skin and cause rash, redness, or pustulated eruptions, like pimples or boils.
This is why skin creams and lotions don’t work in such a scenario. It’s not a skin problem. It’s a problem of chronic blood poisoning from an indigestible diet. Third World people rarely get acne. Acne is a disease of excess, a consequence of the enzymeless, fast food lifestyle.
Chronic ‘incurable’ eczema and psoriasis often fall into the same category. People suffer needlessly for years with these diseases, under the direction of their well-intentioned but clueless dermatologist who has convinced them that their only hope is to find the right medication for their ‘skin disease.’
Same with the kidneys. Their original job was simply to maintain water and electrolyte balance within the blood. But with the advent of modern foods of commerce, suddenly the kidneys find themselves spending all their energy trying to filter out these new manmade chemicals from the blood – a function for which they were never designed. Result: kidney disease today is the #9 cause of death in the US. 
Dr. Henry Bieler offers another example of vicarious elimination: the lungs take over for the kidneys. When the level of toxins in the blood exceeds the kidneys’ capacity to eliminate them via the urine, the lungs try to take up some of the slack. The lungs secrete some of the blood’s toxins through their mucous membranes. Such toxicity irritates and inflames the delicate lung membranes, and can be the initial cause of pneumonia, bronchitis, asthma, edema or virtually any other lung problem. So the lungs detox you by breathing out the volatilized poisons. (p 164) 
Same with a cold. A cold is simply the body’s way of saying that the level of toxicity has now surpassed the body’s ability to get rid of wastes through the normal avenues: colon, kidneys, and liver. So it will try alternative or vicarious routes: nose, mouth, throat, eyes, or lungs.
Bieler uses this same model to explain dysmenorrhea and pelvic inflammatory disease: irritation of female organs when they are used as alternate routes of toxin removal from the blood, every month. At menopause, when this avenue of detox falls into disuse, various new problems may occur as a result. (p 172).
Vicarious elimination: an organ of reproduction being used as an emergency organ of detoxification.
Again, Tilden’s theory of vicarious elimination is that many diseases are really just an organ’s emergency attempt to discharge excess poisons because the primary avenues are overloaded. If that body part is overwhelmed in the process, it becomes diseased and we pretend that that organ, in isolation from the rest of the body, is the problem.
Such thinking is more than just simplistic and disingenuous; if medical decisions are based on false perceptions focusing only on the diseased organ as the disease, the results will range from ineffective to fatal.
Dr. Tilden felt that undigested food in the intestines and in the blood was the primary cause of all disease. His ideas are now being substantiated in most gastroenterology journals, which explore in great detail the ‘modern’ phenomenon of
LEAKY GUT SYNDROME
The reason the food remains undigested is lack of enzymes.
Here’s what happens: We eat trashy food. We can’t digest it. It remains in our intestines in a rotting form for weeks on end. Eventually the protective intestinal lining weakens and allows some of the rotting, undigested food to enter the bloodstream.
Once in the blood, the toxic debris can settle just about anywhere. As a foreign protein, the debris can then initiate an inflammatory reaction at the particular location where it happens to end up. The snap diagnosis is that we have a problem at the site of the inflammation: the joints, the muscles, the liver, the kidneys, the intestines, the stomach, whatever.
Then we are given drugs to cover up the symptoms. Doctors pretend they can treat that single ‘problem’ part in isolation from the rest of the body. That’s why it doesn’t work.
According to Dr. Tilden, these types of chronic, mysterious illnesses almost always have toxemia as the root cause.
Dr. Tilden was ahead of his time. His ideas are far superior to modern drug remedies. In most chronic disease situations, especially one that has baffled all the medical geniuses, Tilden’s approach should be tried first, if one is to have any hope at all of a complete, permanent recovery.
Thomas Sydenham, the most famous English physician of the 17th century, long ago supported Tilden:
“Disease is nothing else than an attempt on the part of the body to rid itself of morbific matter.”
– Bieler, p 40 
Morbific – that means dead and rotting.
For more on the colon see Journey to the Center of Your Colon.