cutaneous pili migrans is a rare condition characterized by a hair fragment or hair shaft moving in the shallow epidermis or dermis , forming an eruption resembling larva migrans . up to date , no more than 30 cases of cutaneous pili migrans have been reported since its first description by yaffee in 1957 , and it has asian predilection . however , we considered that cutaneous pili migrans has been underestimated , because even the present corresponding author and the colleagues had met 4 cases since 2009 . among them , 2 had been previously reported , and another 2 whom were diagnosed recently had not been reported yet . interestingly , there is an exceptionally rare condition previously called  ingrown hair  mimicking the presentations of cutaneous pili migrans , in which the causative factor is a hair growing inside the skin and burrowing in the uppermost dermis rather than a hair shaft moving inside . to our knowledge , only 4 cases published in japanese literature have been reported ( table 1 ) , and none in english literature have been described . herein , we report a case and suggest to rename it as  ingrowing hair . a 30-year - old chinese man without any relevant medical histories was referred because of 1-year history of slowly extending black linear eruption on his right chin , which gradually protracted toward the back of neck without any associations . the patient usually shaved his beard by blade , and was accustomed to pull or extrude the beard hairs when he had spare time . cutaneous examination showed that a 4.3-cm - long black linear eruption beneath the skin located on the right chin , associated with edematous erythema around it and 2 inflammatory papules on both ends of the lesion ( figure 1a ) . after 1-week treatment of topical mupirocin ointment , the edematous erythema and papules improved excellently , and a hair shaft with its distal end protruding out of the skin was observed which was pulled out with ease ( figure 1b and c ) . the hair , measured 4  cm in length , was demonstrated a hair shaft with follicles under microscope ( figure 1d ) . meanwhile , another hair , about 0.3  cm far from the follicle of the priorly pulled beard hair , was also found which showed a short section protruding out of the skin near the root . by pulling the hair near the root with forceps , a 2.2-cm - long , slippery , straight , black hair was easily removed from the skin ( figure 1c , the white arrow ) . however , a new black linear lesion about 1  cm in length appeared in the skin in the region of prior erythema ( figure 1e ) . after a shallow incision of the skin , a 1-cm - long hair with follicles was extracted from the epidermal burrow ( figure 1f ) . the patient was given topical mupirocin ointment for a week , and was asked to stop pulling or extruding the beard hairs . the presentations of ingrowing hair . a 4.3-cm - long black linear lesion beneath the skin located on the right chin associated with edematous erythema around and 2 inflammatory papules on both ends of the lesion ( a ) . the folliculitis improved excellently after treatment with topical mupirocin ointment for a week , and a hair shaft with its distal end protruding out of the skin presented on the lesion ( b ) . a hair ( grasped by the forceps ) ( c ) with hair follicle ( d , the white arrow ; the inset showing a closer view of the hair ,  100 ) is easy pulled out ; the second hair shaft ( c , the white arrow ) with its follicle in skin is pulled out from the skin . a new black linear lesion about 1  cm in length appeared in the skin in the region of prior erythema 2 weeks later after pulling out of the prior beards ( e ) , showing hair shaft with hair follicle ( f ) . based on the entities that the black lines were beard hairs with follicles extending gradually rather than hair shafts moving alone , we considered that the present conditions resulted from the hairs growing inside the skin , and we diagnosed them as  ingrown hair  rather than considering the hairs had been growing inside the skin until they were pulled out , we prefer to term the present instance as  ingrowing hair  rather than  ingrown hair ,  which may be a more appropriate way to describe the disease , and can be distinguished from the condition in pseudofolliculitis barbae in which the hair also grows inside the skin and causes pseudofolliculitis . although the exact mechanisms for ingrowing hair remain unknown , we considered that the actions of pulling or extruding the beard might play important roles for the present patient , because the actions might result in possibility of localized inflammation and edema around the follicle , and/or changing the growing direction of the beard hair , that made the hair grow inside the skin possible . while the hair was growing slowly inside the skin , the black lesion was extending gradually , and the length of lesion may be equal to the length of the ingrowing hair ( excluding the follicle section ) . but when the hair follicle is deceased , the hair might move inside the skin as cutaneous pili migans does . when the hair is growing inside the skin , it may also cause physical stimulation causing possible erythema around . in the present case , a hair shaft extruded out of the skin after the inflammation improved , we thought that the erythema may be a possibly inflammatory reaction stimulated by the hair , and the hair was excluded from the skin as a foreign body finally . of course , we can not exclude the possibility that localized infection played a role in some extent for the erythema . based on the literature , only 5 cases , including the present patient , have been reported and all were men with an age range of 30- to 58-year old ( table 1 ) . the results suggested that ingrowing hair always occurs on the area where the beard hairs are distributed , and beard hairs may be the causative hair . to our knowledge , no similar cases were described in other areas , mimicking cutaneous pili migrans with asian predominance . the reasons of asian predominance for cutaneous pili migrans are because that asian hair , especially the japanese , has larger diameter with circular geometry , and is harder and straighter than african or caucasian hair , which may make the asian hair extend and grow inside the skin easier than that of other population . we speculated that the mechanisms for the asians predilection of ingrowing hair are the same as they are in cutaneous pili migrans . however , we lack the data of any possible difference of the beard hairs between asia and other countries . the differential diagnoses included cutaneous pili migrans , interdigital pilonidal sinus , creeping eruption caused by parasitic diseases , and pseudofolliculitis barbae . cutaneous pili migrans is caused by hair shaft or fragment , or the pubic hair , and always without hair follicles , showing a painful linear lesion with a moving black line at the advancing end . but we speculated that , when the follicle is deceased ,  ingrowing hair  may became  cutaneous pili migrans .  interdigital pilonidal sinus , commonly occurring in the barber , is caused by the naked hair shaft or fragment penetrating the follicle and entering the dermis without extending the lesion . the creeping eruption caused by parasitic disease is always caused by nematode larva , in rare condition , subcutaneous migration of a fly 's maggot ( migratory myiasis ) , an adult nematode ( loa loa , dracunculus medinensis ) , a trematode larva ( f. gigantica ) , or sarcoptes scabiei may be the provoking factors . its lesion is mobile and tracks sinuously , commonly associated with severe itching without presence of black line pseudofolliculitis barbae is an inflammatory disorder that occurs most frequently in men with a dense and curly beard , presenting as the curly hair tending to curl into the skin instead of straight out the follicle . but in rare instance , the hairs come out of and again re - enter the skin causing solid papules with bent hairs inside . based on clinical features , it is not difficult to make a correct diagnosis for such disorders . as ingrowing hair is caused by a hair growing inside the skin , extracting the hair and correcting the bad habit may be its optimal management strategies . the present case is notable because of multiple ingrowing hairs and recurrent lesions . to the best of our knowledge , ingrowing hair is a rare cutaneous disease caused by hair growing inside the skin and characterized by slowly extending black linear lesion beneath the skin , the length of the lesion is always equal to the length of the hair except that inflammatory reaction occurs . it may involve the cheek , chin , and neck , and may be multiple or recurrent . pulling out
abstractcutaneous pili migrans and creeping eruption caused by parasitic diseases may present as a moving linear lesion in skin . 
 the former , caused by a hair shaft or fragment embedded in the superficial skin or middle dermis , is a rare condition characterized by creeping eruption with a black line observed at the advancing end . in exceptionally rare instance 
 , the hair grows inside the skin and burrows in the uppermost dermis , such a condition has been called  ingrown hair.we report a 30-year - old chinese man , who was accustomed to pull or extrude the beard hairs , with 1-year history of slowly extending black linear eruption on his right chin . 
 cutaneous examination revealed a 4-cm long black linear lesion beneath the skin associated with edematous erythema around and folliculitis on both ends of the lesion . 
 after treatment with topical mupirocin ointment , the erythema and folliculitis improved and 2 hairs of the beard with hair follicles were pulled out from the skin . 
 two weeks later , another similar black line about 1  cm in length in the skin presented on the prior lesional area , which was pulled out by a shallow incision of the skin and was also demonstrated as a beard hair with hair follicle.the patient was diagnosed as  ingrowing hair  with multiple recurrences . 
 the lesions recovered after the beard hairs were pulled out . no recurrence occurred in a year of follow-up.we suggest that  ingrowing hair 
 is better than  ingrown hair  to describe such a condition . 
 pulling out the involved hair and correcting the bad practice are its optimal management strategies .