The Golden Period – Dietary Regulation Before Age 1
If we can pay attention to controlling a baby’s diet before age 1 to avoid foods that may trigger allergic reactions, and continue to remind the child after age 2 to avoid scratching areas affected by atopic dermatitis, we can effectively control the symptoms of atopic dermatitis. Therefore, we will first explain the principles and practices of improving atopic dermatitis through reasonable dietary adjustments.
Key to Dietary Improvement – Delaying Exposure to Foreign Proteins
After the body’s immune cells first encounter foreign antigen molecules (including pathogens entering the bloodstream through skin wounds) in local immune organs (such as the skin and intestines), they travel through the bloodstream to lymph nodes, the spleen, or other lymphoid organs, where they initiate an immune response.
Afterwards, these trained immune cells, which can effectively identify and combat the relevant pathogens, will again circulate throughout the body via the bloodstream, eliminating the pathogens or antigen molecules distributed within. Scholars refer to this circulatory process of immune cells within the body as “lymphocyte trafficking.”
Since the skin’s immune system is closely related to the intestinal mucosal immune system, research has found that immune cells originating from the intestinal mucosa also circulate and migrate to the skin’s immune system. Therefore, we can observe that when infants ingest foods that trigger allergies, it is easy to cause atopic dermatitis; and when older, ingesting allergens such as seafood or fruits may cause allergic skin reactions such as urticaria.
The foreign proteins that newborns first encounter usually come from foods, such as formula milk or proteins in other foods (such as egg whites). Years of clinical experience in caring for children with atopic dermatitis has shown that appropriate dietary control and adjustment is far more effective than long-term use of topical medications, highlighting the importance of dietary control for infant atopic dermatitis. However, after 1.5 years old, the link between a child’s skin symptoms and diet becomes less obvious, at which point controlling scratching behavior becomes more important.
The Link Between Skin Allergy and Food Allergy – Improving Through Diet
As mentioned earlier, stimulated immune cells circulate and migrate within the body, ultimately exerting their immune functions at the site of action (such as the skin), triggering a corresponding immune response. Activated immune cells in the intestinal immune organ can reach distal tissues such as the skin via the bloodstream, inducing localized immune responses there. Due to the consistent circulatory migration process of skin and intestinal immune cells, the skin is classified as a mucosal-associated lymphoid tissue in the lymphatic system.
This also explains why intestinal allergic reactions often manifest symptoms on the skin. For example, infant allergies to cow’s milk protein or other proteins can exacerbate atopic dermatitis symptoms; while for adults, the most common symptom after ingesting allergy-triggering foods like shellfish or mangoes is the appearance of hives on the skin. Therefore, dietary control remains an indispensable part of improving skin allergy symptoms.
Although food allergy symptoms may gradually decrease with age due to the development of oral tolerance, it is advisable to avoid foods that may cause allergies, such as milk, proteins, shellfish, and nuts, during infancy to prevent allergic reactions. Then, around 1 or 1.5 years old, these foods can be reintroduced.
Oral Tolerance – An Innate Property of the Immune System
The human immune system is originally designed to combat foreign pathogens, so it will produce an immune response to any foreign protein – this is a fundamental property of the immune system. But you may wonder: “If the immune system reacts to all foreign proteins, wouldn’t the food we ingest daily, like beef or pork, also trigger an immune response?”
In fact, under normal circumstances, this would not happen. Once the human immune system matures, it develops a kind of “tolerance” to proteins ingested orally, without triggering an excessive immune response. This phenomenon is also physiologically reasonable, because food ingested orally is meant to be digested and absorbed as a nutrient source for the body. If the immune system still mounted a significant immune response to these foods, it would be a waste of energy and effort.
During infancy, since the intestinal mucosal barrier function is not yet fully developed, any ingested protein, regardless of food type, can easily trigger a more intense immune response. More importantly, a newborn’s immune system is inherently biased toward a Th2 (Type 2 helper T cell) response, so these excessive immune responses often manifest as allergic reactions.
However, as an individual grows, the intestinal mucosal barrier function will gradually mature, and our immune system will also gradually develop the so-called “oral tolerance” mechanism, resulting in less immune or allergic reaction to food proteins ingested orally later on.
Formation of the Oral Tolerance Mechanism
The development of oral tolerance is related to the establishment of a specialized regulatory mechanism within the immune system. As age increases, the body gradually cultivates a group of cells that can suppress excessive immune responses to orally ingested proteins.
Currently, scholars generally believe that proteins ingested into the intestine induce the emergence of specialized regulatory immune cells, and these regulatory cells can suppress the immune system’s reaction to that protein, thereby achieving so-called “oral tolerance.”
One view holds that under high-dose antigen stimulation, antigen-specific T cells stop activating and no longer respond immunologically to that antigen, which is the essence of oral tolerance. This mechanism is also applied in the current “sublingual immunotherapy” used to treat allergic diseases (such as asthma, allergic rhinitis, etc.). Sublingual immunotherapy involves repeatedly exposing the patient to relatively high doses of the allergen to induce an oral tolerance effect and suppress the allergic reaction.
Due to the existence of oral tolerance, except for a minority of individuals with more specific constitutions, we typically do not experience excessive immune reactions to proteins in our daily diet after growing up. This is the key to dietary control for infant atopic dermatitis – avoiding specific allergy-triggering foods during infancy, and even if the same proteins are ingested later after the oral tolerance mechanism has gradually established, an allergic reaction is less likely to be triggered again. So, parents can be completely reassured.
This is also why clinically it is recommended that the “golden period” for controlling atopic dermatitis is before 1.5 years old. For infants who show allergic symptoms before age 1, parents need to pay special attention to avoiding potential allergenic foods during this stage and actively improve atopic dermatitis symptoms. Once the symptoms are controlled before 1.5 years old, as the immune system’s “oral tolerance” mechanism gradually matures, the child has a high chance of completely overcoming this condition.
The Dynamic Balance of Allergic Reactions and Immune Regulation
From the above introduction to the oral tolerance mechanism, we can see that the human immune system’s response to foreign substances is actually a dynamic regulatory process, not simply a vigorous reaction or complete tolerance.
During infancy, the immune system tends to produce more allergic reactions, mainly due to relatively more active Th2 (type 2 helper T cell) responses. This mechanism may have evolutionary origins, allowing newborn infants to respond more quickly to foreign objects for self-protection.
On the other hand, the body also has a regulatory mechanism called “oral tolerance” to avoid excessive reactions to dietary protein intake, otherwise it would severely waste physiological resources. As an individual gradually grows, the immune system will slowly cultivate oral tolerance, establishing an appropriate level of tolerance for harmless substances.
This dynamic balance of immune response and regulation allows the body to actively respond to harmful invasive molecules while preventing excessive reactions that could lead to self-harm. It can be said that this precise regulation is the essence of the human body’s complex immune system.
Therefore, for the treatment of allergic diseases such as atopic dermatitis, in addition to medication, properly timing the appropriate dietary control, moderate exposure to harmless antigens to establish tolerance, and avoiding continuously triggering allergic reactions is the effective way to provide long-term symptom relief. This requires the cooperation of parents, physicians, and patients to achieve good therapeutic effects.
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