## 1 Introduction  
Research scientists and technicians who work with laboratory animals are exposed to complex mixtures containing both allergens and bacterial endotoxins from animals, bedding and feed [1, 2]. Animals constantly shed proteins via the urine, secretions and desquamation of skin, and these allergens can be released in the air or deposited on surfaces and equipment, so making the animal facility a risky environment for the development of allergies [3]. Endotoxins, lipopolysaccharide-saccharide components of the cell-wall of Gram-negative bacteria with high biological potency in respiratory systems, may also exist in the air of animal units due to the presence of organic material, causing an additional risk for personnel working there. Fecal bacteria in soiled bedding may produce increased concentration of endotoxins, compared to other settings, and this may be an occupational health concern [4]. Workers involved in the direct care of laboratory animals have been shown to be at the highest risk for developing allergies or asthma, likely due to the magnitude of their workplace exposures [5]. Laboratory animal workers (LAWs) have a high risk of developing laboratory animal allergies as a consequence of inhaling animal proteins at work; this occurrence has serious consequences for their health and future employment. Exposure to animal allergen remains to be the greatest risk factor although the dose relation is complex, with saturation at high allergen exposure. Laboratory animal allergy (LAA), especially from mice and rats, is well recognized as causing sensitization and subsequent ocular, nasal, upper and lower respiratory symptoms [6; 7]. The rate of workers that can develop an allergy has been reported with great variability, between 4 and 44% [7; 8; 9; 10; 11; 12; 13; 14]. This variability can also be due to different methodologies used for evaluation. Recent data reported a decrease of LAA (25.6% in 2001-2004 to 8.2% in 2013-2016) probably attributable to preventive programs [15]. In addition to allergens, bacterial toxins also play a role in the allergic process. Inhalation of endotoxins induces health effects mainly on the respiratory system, including decline in lung function and increased prevalence of chronic bronchitis and asthma-like syndrome [16; 17]. Airborne endotoxin has been identified as a major risk factor for nasal, chest and skin symptoms when working with mice in a subgroup of non-mouse sensitized researchers. These findings support an important role for endotoxin as well as mouse allergen in the risk of symptoms and sensitization in the laboratory animal workplace [2]. Rat and mouse allergens (Rat n 1 and Mus m 1) are aeroallergens mainly represented in animal facilities and research laboratories. These allergens were detected on particles of \(>\)5-10 \(\upmu\)a aerodynamic diameter, even if some authors showed the presence of Rat n 1 antigen on particles \(<\) 5 \(\upmu\)m [18; 19]. Airborne Mus m 1 was detected on particles 3.3-10 \(\upmu\)m in diameter in high density mouse rooms [20]. The particle size distribution for endotoxin is unknown, but because endotoxin and mouse allergen have different sizes and charges [21], they may not be associated with the same size particles. However, because both emanate from animal droppings, endotoxin and mouse allergen are likely to be detected together [22]. Other allergens, such as Can f 1, Fel d 1 and Equ c 4, even if they are not related to activity in the animal facility under investigation, may be present in these environments due to the passive transport from life to occupational settings. In fact, a critical issue is the spread of endotoxin and allergens between different environments and tasks characterizing animal facilities and between work and life [23; 24; 25; 26]. As a consequence, environmental monitoring can be useful to distinguish the animal allergens, deriving from the species in the animal facilities, from the domestic species [27].