Question

Lines of Blaschko are:

• A. Lymphatics
• B. Blood vessels
• C. Nerves
• D. Lines of development

Hint:

They trace embryonic skin cell migration, not nerves or vessels.

Answer 1

The Correct Option is D

Step 1: Lines of Blaschko are invisible patterns on the skin that follow the routes taken by epidermal cells (keratinocytes and melanocytes) as they migrate and proliferate during embryonic development.
Step 2: They form a V or fountain shape over the back, S or whorled patterns on the abdomen and flanks, and linear streaks down the limbs.
Step 3: They do not correspond to dermatomes (nerves), to the course of blood vessels, or to lymphatic drainage. This distinguishes them from Langer lines and from dermatomal patterns.
Step 4: They become apparent only in disease, when a mosaic or X-linked skin disorder (such as incontinentia pigmenti, epidermal naevi, or lichen striatus) lays down lesions along these developmental tracks.
Step 5: Hence the lines of Blaschko represent embryonic lines of skin development (lines of cutaneous cell migration).
Conclusion: Lines of Blaschko are lines of development (option 4).