We have already reached Friday, damn and damn! And it shows in the face of more than one who goes on a bridge. With a holiday or not, the Maldita Ciencia office continues to arrive like every Friday to resolve all the doubts that you have raised. This week we collect your questions about the use of exfoliants in tattoos, why some areas of the skin darken, whether it is advisable to urinate after having sexual intercourse and why allergies can appear and disappear over time.

Why can allergies come and go over time?

The reasons behind the appearance of allergic reactions to certain elements in some people and not in others is one of the questions that you have asked us this week. Also because sometimes these allergies disappear in some allergic people. It is a complex issue that does not have a clear answer.

Allergy is a defense reaction of the organism against external substances that enter the body. The body’s immune system recognizes these substances as foreign and attempts to neutralize them but with some negative effects in doing so. People without allergies also recognize them as foreign, but their body neutralizes them without harming itself, through mechanisms called tolerance, explains the Spanish Society of Clinical Immunology, Allergology and Pediatric Asthma (SEICAP) on its website.

For this reason, the origin of an allergic reaction is not therefore in the agent that produces it, known as an allergen, but in the individual himself, the Spanish Society of Allergology and Clinical Immunology (SEAIC) highlights on its website. Antibodies generated by the body as a defense act against these allergens, usually a type called immunoglobulin E (IgE). IgE trigger the release of inflammatory mediators that produce the allergic reaction. People without allergies do not usually form IgE against allergens, but defend themselves by other mechanisms, clarify SEICAP and SEAIC.

And then why do these allergies appear? The truth is that today we do not know. “Answering questions such as why some proteins cause allergies and others do not, as well as why they appear and disappear over time are very difficult questions to answer,” Maria Garrido Arandia, a biochemist specializing in plant allergens and molecular bases , clarifies to Maldita.es of allergic sensitization processes at the Center for Plant Biotechnology and Genomics of the Polytechnic University of Madrid and the National Institute of Agricultural and Food Research and Technology. It is still a mystery for which there is no clear answer”, adds Monica Carreno, a biologist specializing in fish food allergies and the development of vaccines for food allergies at the CSIC’s Marine Research Institute. 

“The allergic reaction occurs because the immune system overreacts to the allergen, a substance that for a large majority of the population is innocuous, and identifies it as a danger,” explains Sara Benede , a technologist at Maldita.es. food and postdoctoral researcher at the Institute for Research in Food Sciences (CIAL) of the Autonomous University of Madrid and the CSIC.

Regarding the ultimate causes, the biochemist Maria Garrido points out that there must be a genetic background, but the presence of another type of environmental signal also seems necessary, such as a tissue injury, a moment of stress or an imbalance in the microbiota, the microorganisms that inhabit our bodies, that causes our body to be altered and we recognize that element as a danger. Once that allergen is recognized as something dangerous, we already create antibodies against that element that “will be responsible for its recognition and all the allergic symptoms,” adds the biochemist, and that will be activated every time we come into contact with it. .

How then does the cure for allergies occur? “In many cases, the allergies that are suffered in childhood and youth disappear with age. The ‘allergic memory’ disappears or the symptoms are attenuated due to a desensitization of the patient to the allergen that has been exposed little by little in a natural way”, Carrera clarifies. Garrido, for his part, points out that in allergic mice to which the allergen was routinely administered, the immune system could be ‘re-educated’ and thus achieve tolerance of the allergen. The immune system manages to tolerate the allergen by enhancing regulatory T and B lymphocytes (immune system cells) and a change in the type of immune response is achieved, Carrera surmised.

“Currently almost all immunotherapies are based on the administration of these allergens to the patient so that in the end the patient gets used to it”, concludes the biochemist Maria Garrido. This type of therapy is commonly known as ” allergy shots ” and is currently marketed to treat asthma, rhinitis, conjunctivitis, allergy to hymenoptera stings such as bees and wasps, allergy to latex and peach skin, collects the SEICAP website. In food allergies, multiple research studies are currently being successfully developed to evaluate the efficacy of immunotherapy with foods such as milk, eggs or peanuts, explains Sara Benede.

Is it true that scrubs ruin tattoos? What do you have to do to take care of them?

Perhaps you have come across a colleague or someone on the internet who says that exfoliants are not recommended for tattooed skin because they deteriorate or even erase them. It’s true? 

Fortunately, this is a myth : exfoliation does not harm healed tattoos, since they work on the epidermis, the outer layer of the skin, and do not affect the tattoo ink, which remains in the dermis, just below. “The fact that the more exfoliation, the more ink you remove is a misconception. It couldn’t be further from reality”, they explain from Tatring , a portal specializing in information on tattoos and piercings. 

As explained by dermatologist Laura Berbegal, exfoliation consists of helping to regenerate the skin “through the elimination of dead cells from the epidermis”. This can be achieved mechanically, “with rough sponges or a horsehair glove”, using chemical products such as creams or acids (glycolic, lactic or salicylic) or a combination of both. “By performing the exfoliation, we help the skin to be smoother, we clean impurities and also prepare it to better absorb the active ingredients that we apply later,” she concludes.

It is for this reason that Tatring recommends including the use of exfoliants as part of tattoo care: “When we get rid of dead cells, we help new skin appear and that is why it feels softer and smoother.” 

On the other hand, the Paper Crane tattoo studio specifies that the exfoliating cream will not cause problems as long as it is completely healed, but in the event that it is still recent or with raised skin, they do not advise rubbing or using exfoliating products. Both the specialized media and Berbegal clarify that it is not advisable to use exfoliants excessively on sensitive areas such as the eye area, the skin of the neckline or —as is obvious— an unhealed tattoo.

And what is the best to take care of a tattoo? The best thing, in the first place, is to follow the instructions of the professional who has done the tattoo, who will offer their advice depending on the tattooed area (if it is more delicate or more exposed), the sensitivity of the skin of each person or other factors. such as allergies or ink used.

Some general recommendations for recent tattoos that the tattoo artist DENO points out to Vogue include washing it “between three or four times a day with clean hands and a glycerin soap”, and always keeping it clean and hydrated so that it heals properly. On the contrary, it is not recommended to expose it during the first days “to the sun, to the water of the pool or beach or to scratch it”. Once it is already cured, it is best to take care of the hydration, use and defend it from solar radiation with protection.

Why do some areas of the skin (such as knees, elbows, hair removal areas such as armpits or moustache) darken?

In all Maldita.es scientific offices we insist that we are not health professionals and that the content we create should never be substituted for a diagnosis or medical consultation. And for this question that you have sent us, it is well reflected: the reasons why these areas of the skin can darken are very broad and only a visit to a dermatologist can determine why this happens, so we cannot offer an answer. concrete.

As we have consulted in Maldita.es the dermatologist Donis Munoz, “I could not give a diagnosis only knowing these characteristics, I would need to see it in consultation and determine what it is exactly.” 

Munoz lists some reasons why these areas of the skin darken: it could be acanthosis nigricans, a disorder in which the skin appears thickened, dark and velvety in folds and grooves on the body and is related to genetic syndromes, obesity and diabetes; hyperpigmentation, a disorder caused by the increase in melanin, which is the pigment responsible for our skin tone, hair, eyes and other parts, and which can be caused by damage from solar radiation, skin lesions or inflammations; or even “some stain that has adhered to the skin and that is hydrosoluble (that goes away with soap and water)”. “It seems strange, but I have come to see people in consultation with this last problem”, he concludes.

In any case, if someone has doubts about whether this is happening to them and suspects that it may be a health problem, our recommendation is that they go to a family medicine appointment and have a professional assess it.

Is it advisable to pee after having sex?

In Maldita.es we already explained why it is advisable to urinate after having sexual intercourse to reduce the risk of bladder inflammation, better known as cystitis. This week you have asked us if, in addition, it can be beneficial for other reasons. The truth is that urinating after having sex is a good idea because it not only reduces the possibility of cystitis, but also other urinary infections. 

These occur when bacteria found on the skin or rectum, for example, manage to infect the urinary tract , the system that allows us to get rid of urine (from the kidneys to the bladder and, finally, out through the urine). the urethra). The most common is cystitis. They are more common in women for obvious reasons: “Their urethras are shorter and closer to the rectum. This makes it easier for bacteria to enter the urinary tract,” says the United States Centers for Disease Control and Prevention (CDC). 

“To prevent urinary tract infections, it is recommended to urinate, at most, between 30 and 45 minutes after having intercourse,” Jose Gomez Cabezas, head of the Obstetrics and Gynecology Service at the Valle de los Pedroches Hospital in the North Health Area , explained to Maldita.es From Cordoba. As the expert adds, there are studies that suggest that “urination after sexual intercourse favors the expulsion of microorganisms and this helps to protect the vaginal flora and the urethra.” In fact, health institutions such as the CDC recommend urinating to prevent this type of infection. 

However, there are studies, such as this one published in 2016 in the scientific journal American Family Physician , which indicate that “postcoital urination appears to have little protective effect”, although it is “a reasonable and safe practice“.  

Sexual intercourse is not the only possible cause of initiation of similar infections. These are more likely to occur if there are changes in the vaginal flora (due to menopause or the use of spermicides, for example), during pregnancy, if there are structural problems of the urinary tract (such as prostate enlargement) or if you have had previous infections. Age also influences : they can occur more easily in both older adults and children. 

To try to prevent them, the CDC recommends staying hydrated; showering instead of bathing; minimize douching, sprays and similar products in the genital area and, in the case of women, after using the bathroom, wipe from front to back and not the other way around.  

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