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Avian influenza, commonly known as bird flu, is an infectious disease caused by influenza A viruses that primarily infect birds. Avian influenza viruses are classified according to their characteristics and the species they infect. Most avian influenza viruses do not infect humans, but some viruses can occasionally cross the species barrier and cause human infections.Human infection with avian influenza was first recognized in Hong Kong in 1997, when highly pathogenic H5N1 viruses infected humans. Since then, H5N1 and other avian influenza viruses have caused sporadic human infections in different parts of the world. Beginning in 2020, a major global spread of highly pathogenic H5N1 among wild birds and poultry also resulted in infections in a growing number of mammals. Human infections remain uncommon, but people who have close or prolonged contact with infected birds or mammals can be at increased risk.Avian influenza viruses can infect many species of birds and some mammals, including poultry and wild birds, as well as mammals such as foxes, skunks, seals, and other animals. Wild birds can carry and spread some avian influenza viruses, sometimes with few or no obvious symptoms, while highly pathogenic strains can cause severe disease and death in poultry and some wild birds. Viruses can spread among animals through respiratory secretions, saliva, feces, and contaminated environments. People can become infected primarily through close contact with infected animals or contaminated environments. Human-to-human transmission of currently circulating avian influenza viruses is considered uncommon, although influenza viruses can change and therefore continue to be closely monitored. Properly cooked poultry [...]

The pH value, or hydrogen-ion activity, is a scale used to describe the acidity or alkalinity of an aqueous solution. More precisely, pH is related to the activity of hydrogen ions in the solution and is commonly expressed on a scale based on the negative logarithm of hydrogen-ion activity.At 25°C, a pH below 7 is generally described as acidic, a pH above 7 as alkaline or basic, and a pH of 7 as neutral. The neutral point can vary with temperature, so pH 7 is not universally neutral at every temperature.There are several methods for measuring pH. Acid-base indicators change color over particular pH ranges, allowing an approximate pH to be determined. pH test strips work on a similar principle and are available in different ranges and degrees of precision. For more accurate measurements, a pH meter uses a pH-sensitive electrode, commonly a glass electrode, to measure the electrical potential associated with hydrogen-ion activity. Properly calibrated laboratory pH meters can provide measurements to considerably greater precision than is normally required for household or field applications. Acid-base titration can also be used to determine the concentration of an acid or base and its neutralization capacity, although titration is not normally a direct method of measuring pH.Because pH affects chemical and biological processes, controlling it is important in many fields:In medicine, the pH of arterial blood in a healthy person is normally maintained at approximately 7.35 to 7.45. Significant deviations from this range can indicate acid-base disorders and may require medical attention. The pH of saliva can [...]

Secondhand smoke is the smoke inhaled when we are in close proximity to a smoker. Secondhand smoke is harmful to both nonsmokers and smokers. According to statistics and analyses, secondhand smoke contains more than 4,000 chemicals, at least 50 of which are carcinogenic; Non-smokers who live with smokers have a higher risk of developing heart disease; children living with smokers are more likely to develop bronchitis and pneumonia; and children—especially infants—who live with smokers are at a higher risk of developing illnesses such as colds, respiratory infections, and ear infections. Compared to the amount inhaled by active smokers, secondhand smoke contains higher levels of carbon monoxide and tar. It contains higher levels of ammonia, benzene, and various other hazardous chemicals. Advertisements for low-tar and low-nicotine cigarettes do not mean they are safer, as they release the same amount of toxic chemicals into the air. Smokers have a higher risk of miscarriage, stillbirth, premature birth, and giving birth to low-birth-weight infants. Therefore, even if we do not smoke ourselves, we still need smoke-free environments in offices, restaurants, and other public places. By Michael Chiu, MWS, CI Previously published in Ming Pao Daily News

Microorganisms can be divided into many different groups based on their characteristics and size, including viruses, bacteria, fungi, algae, and other microorganisms. Fungi include a vast number of species and play an important role in the Earth's ecological environment. They also serve useful purposes in the production of pharmaceuticals and fermented foods. However, fungi can also damage food, homes, and buildings, affecting not only their appearance but also indoor hygiene. Some fungi can cause infections or trigger allergic reactions.Microbial growth generally requires suitable nutrients, moisture, and favorable environmental conditions. Damp environments are particularly favorable for the growth of mold and other microorganisms. Microbial spores are commonly present in the air and can settle on surfaces. When sufficient moisture and other favorable conditions are present, mold can grow and reproduce.Effects on the Human Body: Damp environments are particularly prone to mold growth on food, building materials, and other surfaces. People living or working in damp buildings may be exposed to mold spores and other biological particles, which can irritate the respiratory system and trigger allergic reactions or worsen asthma symptoms. The health effects associated with microorganisms can generally be divided into three categories: infection, allergic reactions, and other effects caused by biological substances or toxins. The severity of these effects depends on the type and amount of exposure and the susceptibility of the individual.People with allergies or asthma, as well as those with weakened immune systems, may be particularly sensitive to mold and other biological contaminants. Keeping indoor spaces dry, repairing water leaks promptly, and removing [...]

高效能空氣微粒過濾器（HEPA）可顯著降低室內空氣中的粒狀物濃度。研究也探討了減少室內粒狀物暴露是否能對心血管健康產生可衡量的益處。丹麥的一項研究調查了21對年齡在60至75歲之間的非吸煙夫婦。這項隨機、雙盲交叉研究讓參與者在48小時內分別暴露於經過顆粒物過濾的空氣和未經過濾的空氣中。研究人員測量了室內粒狀物濃度，並評估了多項健康指標，其中微血管功能是主要結果指標。研究發現，過濾顯著降低了室內粒狀物的暴露量。更重要的是，在過濾期間，微血管功能提高了8.1%（95%信賴區間：0.4%–16.3%）。本研究透過測量暫時限製手臂血流後週邊動脈張力的變化來評估微血管功能。研究結果與其他研究一致，顯示顆粒物暴露會影響血管功能，減少室內顆粒物暴露可能具有可測量的生理益處。然而，本研究樣本數較小，持續時間僅48小時。它測量的是血管功能的指標，而非心血管疾病或心血管事件。此外，研究人員在校正多重比較後，並未發現發炎和氧化壓力等次要生物標記存在統計意義上的顯著變化。因此，這些結果應被視為減少粒狀物暴露可能具有短期心血管益處的證據，而非證明高效空氣過濾器（HEPA）可以預防心血管疾病。後續研究提供了更多證據，表明室內空氣過濾可以影響心血管指標，儘管不同研究的結果並不完全一致，並且[...]

氡是一種天然存在的放射性惰性氣體，無色、無味、無臭。氡主要透過地基裂縫和開口、建築接縫、管道周圍的縫隙以及與地面接觸的地板和牆壁上的其他開口進入室內空間。因此，地下室和建築物中其他靠近土壤的區域氡濃度可能較高。然而，任何房屋都可能出現氡濃度升高的情況，無論房屋是新建還是老舊，密封性好或通風不良，也無論是否有地下室。長期暴露於高濃度氡的主要健康風險是肺癌風險增加。歐洲、北美和中國的研究證實，住宅氡暴露是導致肺癌的因素之一。在加拿大，氡暴露估計導致約16,100兆人死於肺癌。一些家庭的飲用水來自地下水源，例如泉水和水井。地下水流經含有天然鈾和鐳的岩石和土壤時，可能會含有氡。氡會從水中釋放到室內空氣中，特別是在淋浴和其他家庭活動中使用水時。然而，土壤氣體通常是室內氡的主要來源。有幾種方法可以降低室內氡濃度，包括密封主要入口通道和在適當情況下改善通風。但是，當氡濃度較高時，這些措施可能不足以解決問題。降低現有房屋氡濃度最常見且有效的方法是[...]

研究表明，接觸含氯游泳池，尤其是室內游泳池，可能會刺激呼吸系統，並加重部分人口的氣喘症狀。專家提醒游泳者，在運動時不應忽視此潛在因素。氯是消毒游泳池水、防止致病微生物傳播的必要成分。然而，當氯與汗水、尿液、污垢以及游泳者帶入水中的其他物質發生反應時，會生成一種名為氯胺的化學刺激物。這些化合物會在室內游泳池上方的空氣中積聚，並可能引起咳嗽、喘息等呼吸道症狀，尤其容易導致氣喘患者出現這些症狀。研究人員特別關注這個問題，因為游泳通常被推薦為氣喘患者的運動方式。因此，在考慮游泳益處的同時，也應注意泳池水質和周圍空氣品質。適當的泳池維護、充足的通風以及良好的游泳者衛生習慣有助於減少氯胺的生成和積聚。游泳池周圍有強烈的化學氣味並不一定意味著泳池中氯含量過高。熟悉的「氯氣味」通常是由氯胺而非遊離氯本身引起的。若泳客聞到強烈的化學氣味，或出現咳嗽、喘息、眼睛刺激或其他呼吸道症狀，應立即通知泳池運作者。在某些游泳場所，異味也可能來自其他區域，因此游泳者應考慮整個游泳環境，而不應想當然地認為強烈的氣味就一定意味著泳池水中氯含量過高。作者：Michael Chiu，MWS，CI。本文先前發表於《明報》[...]

安大略省居民經常透過媒體了解到安大略省的空氣品質健康指數 (AQHI) 和安省政府發布的空氣品質警報。與美國空氣品質指數 (AQI) 不同，安省的 AQHI 是一個基於健康的等級，從 1 到 10+，根據地面臭氧、細懸浮微粒 (PM2.5) 和二氧化氮的濃度計算。數值越高，潛在的健康風險越大。安省的空氣污染源既有本地的，也有遠距離的。污染物可以跨越省界和國際邊界傳播，包括來自美國，而諸如空氣停滯等天氣狀況會導致污染物積聚。野火煙霧也已成為安省乃至整個加拿大細懸浮微粒污染日益重要的來源。地面臭氧和顆粒物是煙霧的重要組成部分。當氮氧化物 (NOx) 和揮發性有機化合物 (VOCs) 在陽光下發生反應時，就會形成地面臭氧。它不同於平流層中的臭氧層，臭氧層保護地球免受有害紫外線輻射。顆粒物可以直接來自汽車廢氣、工業活動、農業、建築、道路揚塵和木材燃燒等源頭，也可以在大氣中與其他污染物發生化學反應而形成。空氣污染仍然是加拿大和整個北美地區重要的健康議題。交通運輸、工業活動、發電、居民木材燃燒、農業和野火煙霧都會導致人們接觸空氣污染物。這些污染源的相對重要性因地點和季節而異。有證據表明，短期和長期暴露於空氣污染都會損害人體健康。細懸浮微粒與心血管疾病和[...]

自1970年代以來，北美住宅的設計越來越注重節能和氣密性，採用了更有效率的節能門窗、隔熱材料和建築圍護結構。這種設計的優點在於減少了冷熱空氣的流失，從而節省能源。但缺點是，如果通風不足，密封性好的住宅室內空氣品質可能較差。空氣中懸浮的氣體和粒狀物是造成室內空氣品質不佳的主要因素。常見的家庭污染源包括烹飪油煙、油漆、木製家具、家用清潔產品、美容產品、加濕器以及取暖或烹飪設備的燃燒產生的廢氣。灰塵、花粉和其他顆粒物也可能附著在回家的家人的衣物和鞋子上進入室內。如果沒有足夠的通風、過濾和污染源控制，一些室內污染物就會積聚，並可能導致刺激、過敏或呼吸系統疾病。作者：Michael Chiu，MWS，CI。本文原刊於《明報》，並於2026年更新修訂。

最新研究證實，空氣污染會對人體健康造成危害，長期或高濃度暴露會導致過早死亡。空氣污染源眾多，其中粒狀物和臭氧是影響人體健康最重要的污染物之一。汽車廢氣、工廠和發電廠排放物以及室內外木材燃燒產生的煙霧都是粒狀物和其他空氣污染物的重要來源。臭氧濃度越高，對人體健康的風險就越大。臭氧是一種活性極強的氧化性氣體，會刺激呼吸系統，加重現有的呼吸系統疾病。研究表明，臭氧會導致呼吸困難、咳嗽和氣喘發作。兒童、老年人以及患有氣喘或其他呼吸系統疾病的人對臭氧尤其敏感。空氣中的顆粒物也會對健康造成嚴重影響，尤其是在長期暴露於高濃度顆粒物的情況下。細懸浮微粒可以深入肺部，與心血管疾病、呼吸系統疾病、肺癌和過早死亡密切相關。顆粒物污染也會加重氣喘和其他呼吸系統疾病。人們應該認識到減少空氣污染暴露和保護環境的重要性。及早預防和有效控制污染至關重要。對於室內空氣，減少污染源、在適當情況下提供充足的通風以及使用合適的空氣清淨器，也有助於減少接觸空氣中的粒狀物。作者：Michael Chiu，MWS，CI。本文原載於《明報》，2026年更新修訂。