Linea nigra

Author: Juhee Roh, Medical Student, University of Auckland, Auckland, New Zealand. DermNet NZ Editor in Chief: Adjunct A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. July 2018.


What is linea nigra?

Linea nigra is a physiological form of hyperpigmentation commonly seen in the first trimester of pregnancy [1–3]. It is a dark vertical line that runs down the middle of the abdomen and it can be one of the earliest indicators of pregnancy [1,3]. It is also known as the ‘pregnancy line’.

Linea nigra

Who gets linea nigra?

Linea nigra occurs in more than 90% of pregnant women, and is often in association with hyperpigmentation of nipples, areola, and genital areas [2,4–8].

Pregnancy-related hyperpigmentation is prominent and more common in women with darker complexions (Fitzpatrick skin types 4–6) compared to fair-skinned women (Fitzpatrick skin type 1 or 2) [2,9].

Linea nigra can also affect men and children.

A study involving 1550 Nigerian patients reported:

  • The incidence of linea nigra was 92.0% in pregnant women and 16.0% in non-pregnant women [7].
  • Linea nigra affected 80% of men older than 50 years of age who had benign prostatic hyperplasia or prostate cancer.
  • There was an increasing incidence with age in children, reaching a peak of 45% between 11 and 15 years of age [7].

What causes linea nigra?

Linea nigra and other forms of pregnancy-related hyperpigmentation are due to placental hormones, metabolic factors and immunological factors [10].

  • Increased production of melanin is due to the effects of oestrogen, augmented by progesterone [1–3,6,11].
  • Oestrogen activates intracellular oestrogen α- and β-receptors located in in the skin, stimulating melanocytes to increase melanin output [11].
  • Melanin is deposited in the epidermis and taken up by dermal macrophages [2].
  • The placenta also produces bioactive sphingolipids, which upregulate melanogenic enzymes such as tyrosinase and tyrosinase-related proteins 1 and 2 [3].

It is no longer thought that α– and β–melanocyte-stimulating hormone from the pituitary gland causes hyperpigmentation during pregnancy [3].

What are the clinical features of linea nigra? 

Linea nigra is a linear band of macular hyperpigmentation that extends vertically down the midline of the abdomen [13,14].

  • Linea nigra usually extends from the symphysis pubis (the cartilaginous joint between the pubic bones) to the umbilicus (the belly button), but it can extend further up to the xiphoid process (the lowest point on the sternum) [4,6,9,11].
  • Hyperpigmentation can range from a slight shade of brown to a grayish black [10, 12]. It may darken following sun exposure.
  • The width of linea nigra is usually around 1 cm; it is consistent in width along its entire length [14].
  • Linea nigra can increase in width and intensity throughout pregnancy.
  • It is often accompanied by the 'ligamentum teres sign', when the umbilicus deviates to the right [3].

How is linea nigra diagnosed?

Like other cutaneous physiological changes of pregnancy, linea nigra is diagnosed clinically [2]. No specific tests are necessary.

What is the differential diagnosis for linea nigra?

Occasionally, other forms of localised hyperpigmentation may be considered in the differential diagnosis of linea nigra [9].

Other pigmented conditions that may occur on the abdomen include:

What is the treatment for linea nigra?

There is no specific medical treatment for linea nigra [14]. Women can be reassured that linea nigra has no adverse effect on pregnancy outcomes, and medical treatment is not required [18]. Affected women should avoid sun exposure to the abdomen, as this might cause the line to become darker.

It has been suggested that folic acid reduces the formation of linea nigra. Folic acid can be found in foods such as leafy green vegetables, oranges and whole wheat bread [2]. Bleaching has been used in some cases, with unsatisfactory results [13,19,20].

What is the outcome for linea nigra?

Linea nigra usually gradually fades over time after delivery, but some women may have persistent hyperpigmentation [1–3]. It can reappear with subsequent pregnancies [14].

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References

  1. Soutou B, Régnier S, Nassar D, Parant O, Khosrotehrani K, Aractingi S. Dermatological manifestations associated with pregnancy. Medscape
  2. Vora RV, Gupta R, Mehta MJ, Chaudhari AH, Pilani AP, Patel N. Pregnancy and skin. J Family Med Prim Care 2014; 3: 318–24. PubMed Central
  3. Kar S, Krishnan A, Shivkumar PV. Pregnancy and skin. J Obstet Gynaecol India 2012; 62: 268–75. PubMed
  4. Bieber AK, Martires KJ, Stein JA, Grant-Kels JM, Driscoll MS, Pomeranz MK. Pigmentation and pregnancy: knowing what is normal. Obstet Gynecol 2017; 129: 168–73. DOI: 10.1097/AOG.0000000000001806. PubMed
  5. Bolognia JL, Schaffer JV, Duncan KO, Ko CJ (eds). Dermatology essentials. London: Elsevier Health Sciences, 2014. 
  6. Black M, Rudolph CA, Edwards L, Lynch P. Obstetric and gynecologic dermatology, 3rd edn. Oxford: Elsevier, 2008.
  7. George AO, Shittu OB, Enwerem E, Wachtel M, Kuti O. The incidence of lower mid-trunk hyperpigmentation (linea nigra) is affected by sex hormone levels. J Natl Med Assoc 2005; 97: 685–88. PubMed Central
  8. Kumari R, Jaisankar TJ, Thappa DM. A clinical study of skin changes in pregnancy. Indian J Dermatol Venereol Leprol 2007; 73: 141. Journal
  9. Perkins A, Levin N, Bernhard JD, et al. Linea nigra — Skin. Available at: https://www.visualdx.com/visualdx/diagnosis/linea+nigra?diagnosisId=54406&moduleId=7 (accessed 18 June 2018).
  10. Braun-Falco O, Plewig G, Wolff HH, Burgdorf WHC (eds). Braun-Falco's dermatology, 2nd edn. Berlin/Heidelberg/New York: Springer-Verlag, 2000. 
  11. Okeke LI, George AO, Ogunbiyi AO, Wachtel M. Prevalence of linea nigra in patients with benign prostatic hyperplasia and prostate carcinoma. Int J Dermatol 2012; 51 Suppl 1: 41–8. DOI: 10.1111/j.1365-4632.2012.05564.x. PubMed
  12. Elling SV, Powell FC. Physiological changes in the skin during pregnancy. Clin Dermatol 1997; 15: 35–43. DOI: 10.1016/S0738-081X(96)00108-3. Journal
  13. Hyperpigmentation and melasma. In: Ingber A. Obstetric dermatology: a practical guide. Berlin/Heidelberg: Springer-Verlag, 2009: 7–18. 
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  15. James WD. Cafe au lait spots. Medscape. 2018. Available at: https://emedicine.medscape.com/article/911900-overview (accessed 18 June 2018).
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  17. Tallon B. Flagellate erythema. DermNet NZ. 2007. Available at: https://www.dermnetnz.org/topics/flagellate-erythema (accessed 18 June 2018).
  18. Massinde A, Ntubika S, Magoma M. Extensive hyperpigmentation during pregnancy: a case report. J Med Case Rep 2011; 5: 464. DOI: 10.1186/1752-1947-5-464. PubMed
  19. Wade TR, Wade SL, Jones HE. Skin changes and diseases associated with pregnancy. Obstet & Gynecol 1978; 52: 233–42. PubMed
  20. Blereau RP. Three cases of hyperpigmentation of pregnancy. Modern Medicine Network. 2002. Available at: www.patientcareonline.com/endocrine-diseases/three-cases-hyperpigmentation-pregnancy (accessed 18 June 2018).

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