BACKGROUND: Many factors, including sex, genetic predisposition, UV exposure, seborrhea and ageing are known to cause enlarged pores. However, very few is known about changes affecting the tissue surrounding the pores with age and about differences in different ethnic group. This study aimed at characterizing the pores structures and their environments in relation to age and ethnicity.

METHODS: the target study population was 160 women of different ethnicities (Caucasian; Hispanic; Asiatic and fro-American) subdivided in 2 age groups, between 15 to 35 yo for the youngest and 45 to 65 yo for the eldest, presenting small or large pores according with grade 1 & 2 amd grade 3 & 4 of the Roland Bazin Atlas of pores, respectively, in the same proportions (50-50) between the groups.
After acclimation, on the right cheek of each subject, clinical and in vivo microscopic imaging was performed by means of standardized photography (parallel polarized and crossed polarized macroscopic images of the skin using a NomadCam from Newtone Technologies), in vivo reflectance confocal microscopy (RCM) (Vivascope 3000). and OCT imaging (Vivosight).
Upon RCM, epidermal and superficial dermal structures, including follicular and perifollicular structures and stroma aspects were described. Skin architecture, sebaceous glands, follicular pattern and intensity of vasculature signal were evaluated on OCT images, whereas signal intensity of superficial and deep dermis and average size of sebaceous glands were measures through an OCT dedicated software. 
Chi-square test and t-test were applied on binary/ranked evaluations and continuous measures respectively. P<0.05 was considered statistically significant.

RESULTS: Overall, small pores (Bazin 2 or smaller) compared with large pores (Bazin 3 or greater) more frequently showed the perifollicular epidermal invagination upon OCT. Moreover, stroma signal intensity around the follicle resulted higher and with a smaller attenuation in small pores compared to large ones. Sebaceous glands were larger in large pores, statistically borderline.
Considering only the younger subgroup, in large pores shape of the hair follicle was more irregular/elongated, and stroma fibers were more frequently coarse/huddled upon RCM; Also, bright tubular structures surrounding the hair follicle were more evident in large pores, but only in young Caucasian volunteers. On the other hand, elder subjects showed wider width of hair shaft by OCT and more regular keratinocytes by RCM in large pores.
Concerning age-dependent differences, only irregular keratinocytes and coarse/huddled collagen resulted significantly higher in elderly.
Concerning ethnicity-dependent differences, Asiatic and Afro-americans showed at OCT larger width of hair shaft, higher intensity of stroma around the follicle, with higher attenuation in Afro-american only, and at RCM reticular stroma fibers around the follicles. Larger sebaceous glands at OCT, and more frequent presence of bright tubular structures at RCM were observed in Asiatic skin.

DISCUSSION: appearance of large pore is predominantly occurring with age, but also detectable in young subjects. Some inflammatory phenomena, follicular/sebaceous gland diseases, degenerative events, genetic and racial predisposition, UV exposure were considered causes of this process. However, no study has been conducted so far to explore the structural microscopic alterations detectable in different age groups and ethnicities. In this study we explored the microscopic aspects of the skin in vivo combining RCM and OCT imaging with complementary resolution and depth properties. RCM and OCT enable cytological and architectural level resolution and revealed the presence of higher stroma signal intensity around the hair follicle in small pores, along with a more evident peri-follicular invagination and larger sebaceous glands. In younger subjects presence of coarse/huddled collagen was more evident in large pores. These results suggest that the appearance of large pores is related with stroma structure modification surrounding the hair follicle, resulting in less intense stroma signal around the follicle upon OCT, and reduction of thin reticular fibers in young skin, followed by loss of epidermal tension in proximity of the follicle (resulting in the epidermal invagination as consequence of focal epidermal laxity). Concerning ethnic differences, stroma was more intense and with more reticular fibers in Asiatic and Afro-american subjects, whereas larger sebaceous glands and bright tubular structures were observed in Asiatic skin.
In conclusion, stroma structural changes seems to be responsible of generation of large pores and consequent perifollicular laxity of skin. This event is likely independent from ethnicity or age, although skin structural differences are observed in different ethnic groups.

Skin microscopic alterations related to large pores studied in different ethnic groups studied by Confocal Microscopy and Optical Coherence Tomography