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Allergies or allergic reactions are exaggerated and inappropriate responses of the immune system to a foreign substance that for most people is harmless.

The immune system is capacitated to defend our body against attacks by foreign substances. However, in some people it mistakenly identifies certain substances as being more dangerous than they actually are and causes several adverse and harmful reactions, such as sneezing and itching that we normally associate with allergic reactions. Even though these substances are generally tolerated and accepted by most people’s organisms. The substances that cause an allergic immune reaction are called allergens.

Allergens can come from a variety of sources and trigger an allergic reaction in several ways:

Aeroallergens (inhaled): include pollens, animal hair, dust mites, etc.;
Food (ingested): include milk and egg proteins, seafood or dried nuts, etc.;
Medicines (ingested or topical): include antibiotics, painkillers, anti-inflammatories, etc.;
Poison (sting): include insect poisons such as bees, wasps or mosquitoes, etc.;
By contact (touch): include metals, latex, perfumes, parabens, etc.;

While some people are only sensitive to a single substance, thus having an isolated allergy to a certain thing, others are sensitive to several substances. The reaction level also varies not only from person to person, but also from substance to substance. While some reactions are just inconvenient, they may sometimes be extreme and potentially fatal, these are called anaphylactic reactions.

A person is not born allergic. There must be a combination of genetic and environmental factors for the development of an allergy. Allergies are therefore potentially hereditary, that is, if a parent suffers from a certain allergy there is a 50% probability that it will be passed on to the child, but if both parents have that same allergy the probability increases to 75%. This means that the child has a higher predisposition for this allergy, not the allergy itself, which is only triggered by environmental factors.

Environmental factors also increase the risk of developing a new allergy throughout life. These environmental and risk factors include:

• Prolonged exposure to foreign substances (allergens);
• Diet;
• Pollutants.

Exposure to these foreign substances, enhanced by the importance of genetic inheritance, can trigger allergies, however, exposure to various bacteria and viruses, especially during childhood, can even strengthen the immune system. This exposure teaches the body to react to the presence of allergens in a controlled and non-harmful manner, thus helping to actually prevent the development of allergies or at least to mitigate their intensity. Conversely, a sterile environment that limits a child’s exposure to bacteria and viruses, even if it seems to be the logical action to take, may even increase the risk of developing allergies. The early use of antibiotics is also associated with a potential risk of developing allergies.

1. Allergy to pollens

Allergy to pollens is generally considered to be a seasonal allergy, due to the fact that it is associated with allergic reactions to aerial particles of pollen that are released during the breeding season of plants, varying from region to region this usually occurs between the spring and summer and sometimes autumn.

A person may suffer from allergic reactions to pollens from one or more plants, this means that the critical period for their allergies may be more or less prolonged. That is why pollens are considered to be the most active environmental allergens in triggering allergic reactions in the general population.

Pollens are one of the methods for plants to reproduce. They are extremely small or microscopic grains generated by the male plants. Plants have evolved so that their pollens are able to cover huge distances, covering many kilometers carried out by the wind or pollinating insects (such as bees), so it is possible to find pollens in all outdoor environments. Yet, they are dependent of atmospheric conditions, with temperature and humidity playing a key role in their dissemination. These conditions are most favorable during the spring and summer months, coinciding to when the symptoms are more aggressive. With the arrival of rain, pollen levels are drastically reduced.

In Portugal, pollens are present in our atmosphere virtually all year round, even during the winter months. The peak occurs in the period between May and July.

The most common symptoms are itchy nose, roof of the mouth, throat and eyes, runny nose and / or nasal obstruction, coughing, irritability and difficulty sleeping.

2. Allergy to dust mites

Mite allergies can be considered as allergies to household dust. For the reason that domestic dust is composed of several particles of potential allergens, among which are mites or more precisely the excrement of mites, but also mold, fungal spores, fabric fibers, animal hair and insect particles. This is a kind of allergy that is present all year round, without any relation to the seasons, even though during the winter months it can trigger more serious symptoms due to the fact that we spend more time indoors.

In Portugal, where the climate is mild, mites have fertile ground for their reproduction. This is because the temperature range for their reproductive cycle is between 5ºC and 30ºC, with the optimal temperature being around 20ºC. Therefore, since in Portugal we don’t have very harsh winters or very high temperatures, mites reproduce in abundance. Dust mites are usually present in the dust that accumulates on carpets, bedding, upholstered furniture and soft toys.

This kind of allergy is usually associated with nasal symptoms such as allergic rhinitis and asthma, though sometimes allergens are inadvertently rubbed into the eyes, in which case they can trigger allergic conjunctivitis.

3. Food allergies

Food allergies are allergic reactions to a certain food or some compound of that food, usually proteins. This type of reactions may vary from mild to very severe (anaphylactic reaction).

Although food allergies may occur at any age, they are more likely to occur during childhood. Since this is a type of allergy that can be overcome during growth, it is less common in adults. However, if it persists into adulthood, the likelihood of being surpassed greatly decreases.

We should not confuse allergic reactions to food with other reactions that food may as well trigger. For instance, food intolerance is not an allergic reaction due to the fact that instead of being an exaggerated response of the immune system it is a reaction of the gastrointestinal system that results in a digestive disorder, that is, the inability to digest a certain food.

Any food has the potential to prove to be an allergen to a certain person and thus triggering an allergic reaction. However, some foods have proved to be more common in doing so and that varies according to the age group.

In babies and children, the foods most associated with food allergies are:

• milk
• eggs
• wheat
• peanuts and other nuts
• Soy

In Portugal, milk and eggs are the first and second causes, respectively, of food allergies diagnosed in babies and children. However, they tend to be transitory.

In adolescents and adults, the foods most associated with food allergies are:

• nuts
• shellfish

In Portugal, given our Mediterranean diet, we are very exposed to shellfish, which includes crustaceans (shrimp, crab, lobster, barnacles, etc.) and mollusks (clams, mussels, etc.). These allergies are more common in adults, but are not limited to this age group. Dried nuts are also strongly associated with food allergies and the reactions they trigger have the potential to be quite serious.

In food allergies, once we ingest the food the reaction comes from the inside out. Here we can see rashes or eczema, nausea, vomiting and diarrhea or itching in the mouth and throat. These are considered to be mild to moderate reactions. In food allergies, there is a higher danger of more aggressive reactions, called anaphylactic reactions, which can be fatal due to the fact that the throat and respiratory airways can swell to the extent that breathing is impossible.

4. Allergy to insect bites

Insect bites may trigger two types of responses: immunological and non-immunological. Immunological responses, as previously mentioned, are the overreactions of our body’s defense system against foreign substances, in this case the venom present in the bite of wasps, for instance. Non-immunological responses are responses of the skin or other tissues to the insect’s bite itself, which can be called an exaggerated hypersensitivity, but not an allergy, here we usually find the bites of mosquitoes and fleas.

Since insects are more present during the months between spring and summer (also associated with the plant breeding season), there is a seasonal window for a higher incidence of these allergies.

The most common symptoms of the poison present in insect bites are generally quite benign and mostly mild. We may develop localized pain, itching and redness and even swelling where the bite took place. Nonetheless, certain poisons have an increased potential to trigger severe allergic reactions (anaphylaxis) and are usually associated with bee and wasp stings.

5. Allergy to medicines

Allergy to medicines is the exaggerated and disproportionate reaction of our immune system to some compound present in the composition of the medication we took. However, as with insect bites, not all adverse reactions can be considered allergic reactions. Here we may include, for instance, the stomach discomfort associated with taking aspirin which, even though it is an adverse reaction, does not mean that the person is allergic to aspirin.

This is a kind of allergy is considered relatively uncommon and not usually associated with the amount of medication taken, nonetheless the reactions may vary from mild to very serious and potentially fatal. Even a small amount is sufficient to trigger an allergic reaction and the fact that we are incapable of predicting them is quite dangerous. Only after taking the medicine will we able to know if we are allergic or not. For this reason, doctors always ask if we are allergic to any medication, so they know what they can or can’t prescribe you. Some emergency medications such as penicillin are the most worrying, since the patient is often not in a position to inform the paramedic in an emergency situation. It is therefore advised to people who already know if they are allergic to certain medicines to carry an alert bracelet with their allergy’s information.


The person best suited to diagnose and deal with allergies is the doctor who specializes in Immunoallergology. After the suspicion of an allergy and a medical examination, the doctor will be able to carry out specific and complementary tests, such as skin tests, exposure tests and laboratory tests.

Once the source of the allergic reaction has been identified, measures can be taken to prevent contact or exposure to the allergen, thereby preventing symptoms. However, we are not always able to prevent this contact or exposure, as is the case with allergies to pollens that circulate in the air where we pass. In the case of food or medicines allergies this can be an effective strategy, considering that we are caution at all times.

If we are unable to avoid the allergens, there are certain measures that we can take such as antihistamine medicines that relieve allergy symptoms. One other treatment, considered to be more effective, is specific immunotherapy, that is a concentrated treatment that works like a longer-lasting vaccine.

A treatment for allergies can also be to induce tolerance, in which small doses of the allergen are administered gradually to the patient, thus increasing the body’s tolerance to it and preventing an initial reaction with a high dose that can become an anaphylactic shock. It is a procedure generally associated with food allergies, such as milk and eggs, in children.

It is important to highlight the potential for the severity of allergic reactions and their associated complications, so any suspicion, diagnosis and possible treatment must be taken with the utmost seriousness and accompanied by a doctor specialized in Immunoallergology.

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