Hair products are commonly used to maintain hair health or cosmesis. Products applied to the scalp and hair contain multiple active and inactive ingredients that can potentially cause irritant and/or allergic contact dermatitis. The objectives of this study were to identify and to discuss the most common allergens in scalp and hair applied products causing scalp allergic contact dermatitis (ACD). A PubMed search identified 99 studies, with 3185 patients and 31 categories of scalp products. Hair products reportedly associated with scalp ACD were hair dyes (41%), shampoos (28%), and conditioners (22%). The most commonly reported patch test–positive allergens were p-phenylenediamine (23%), nickel (15%), fragrance mix (13%), balsam of Peru (10%), cocamidopropyl betaine/3-dimethylaminopropylamine (7%), and methylchloroisothiazolinone/methylisothiazolinone (6%). Common symptoms and signs include eczematous lesions, pruritus, and a burning sensation. Medical practitioners should be aware of causative agents to provide appropriate patient education, counseling, and/or treatment.
<b><i>Introduction:</i></b> The prevalence of frontal fibrosing alopecia (FFA) is increasing worldwide, though the pathogenesis remains unknown. Anecdotal reports describe alopecia occurring in an FFA pattern following facial surgical procedures, but this potential link remains unexplored. <b><i>Objective:</i></b> The objective of this study is to determine if a significant association exists between the diagnosis of FFA and a history of facial and scalp surgical procedures. <b><i>Methods:</i></b> This retrospective study comparing data from frontal alopecia patients to controls was conducted at a tertiary medical center. Additionally, a literature review was conducted on scarring alopecias occurring from scalp procedures. <b><i>Results:</i></b> Fifty percent of frontal alopecia patients (<i>n</i> = 54) reported a history of facial surgical procedures compared to 9.8% of controls (<i>n</i> = 51) (OR: 7.8 [95% CI: 2.77–25.98, <i>p</i> < 0.001]). Although no significant differences were observed in current daily facial sunscreen use, sunscreen use prior to alopecia onset was significantly higher in frontal alopecia (<i>p</i> = 0.295; <i>p</i> = 0.021). Sunscreen use was not a significant modifier in the association between frontal alopecia and facial surgical procedures (<i>p</i> = 0.89). <b><i>Conclusions:</i></b> A significant association exists between frontal alopecia clinically consistent with FFA and a history of facial surgery, the nature of which is unclear. The role of sunscreen use and frontal alopecia development in this setting needs to be better elucidated.
Measurement and quantification of cadaveric nasal hairsDear Editor, Nasal hairs, known as vibrissae, serve as a filtration system to prevent particles larger than 3 µm from passing through the nasal cavity. 1,2 Patients with alopecia areata (AA) often have associated loss of vibrissae, resulting in vasomotor discomfort and rhinitis, and are at hypothetical risk for increased inhalation exposure to environmental allergenic and infectious aerosolized particles. 3 Surprisingly, there is no evidence in literature on any anatomic description of human nasal vibrissae characteristics.
We addreas the problem of training neural networks to act as approximations of continuous mappings. In the case where the only representation of the mapping within the training process is through a finite set of training points, we show that in order for this set of2 points to provide an adequate representation of the mapping, it must contain a number of points which rises at least exponentially quickly with the dimension of the input space. Thus we also show that the time taken to train the networks will rise at least exponentially quickly with the dimension of the input. We conclude that if the only training algorithms available to us rely upon a finite training set, then the application of neural networks to the approximation problem is impractical whenever the dimension of the input is large. By extrapolating our experimental results, we estimate that 'large' in this respect means 'greater than ten'.
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