Differences between Darker and Lighter Skin Tones

00:01 Now we want to take a look at the differences in skin color.

00:05 Looking at the epidermis, the melanocytes, the dermis and hair.

00:11 If we focus on the epidermis, what are some of the differences in melanin rich and melanin poor skin types.

00:20 On the epidermis.

00:23 So if you look at the stratum corneum as part of the epidermis, as we have spoken about that in our previous lectures, in light skin or melanin poor skin, there's about 17 cell layers.

00:38 However, the dark skin has got about 22 cell layers.

00:43 Same thickness, but then the cells are more compact in dark skin.

00:51 So, as explained, because of the thicker layers in the dark skin, it makes it stronger when exposed to mechanical or chemical stress.

01:04 The other second difference is increased transepidermal water loss and decreased ceramides. This will also find in people with melanin rich skin.

01:20 So the combination of increased transepidermal water loss and decreased ceramides make the skin more prone to dehydration and make the skin drier.

01:35 And this can lead to a condition called xerosis, which means dry skin.

01:41 And xerosis and atopic dermatitis are also seen more commonly in melanin rich skin.

01:49 The second point I want to talk about in terms of the differences between melanin rich and melanin poor skin, is melanocytes and the melanin.

02:01 The number of melanocytes is the same in all skin types.

02:07 The main difference is in the melanosomes and melanin.

02:12 So physiologically, anatomically the skin is the same.

02:16 But the difference that gives us our different skin color is the melanosomes and melanin. We are now going to zoom in on melanosomes to try and find out what are the differences between the two skin types in light skin.

02:30 The lower number of melanosomes in dark skin.

02:33 There's a higher number of melanosomes in light skin.

02:36 They are small and aggregated, and in dark skin they are larger and non-aggregated.

02:41 They are mostly confined to the basal layer, whereas in dark skin they are distributed throughout the epidermis, as you can see on that picture, there's a faster degradation rate in light skin and a lot slower degradation rate in dark skin.

02:55 So now I want to talk about melanin in light skin.

02:58 We've got a lower melanin content.

03:00 And in dark skin we've got a higher melanin content.

03:03 And of course a lower rate of melanogenesis compared to dark skin due to the previously mentioned properties.

03:11 Talking about melanosome size and melanin content, the dark skin provides better photoprotection five times less UV light reaches the upper dermis in black skin compared to a lighter skin.

03:25 So the advantages of higher photoprotection in dark skin.

03:29 One of the advantages, actually, is that you tend to get delayed aging and reduced wrinkling in patients with melanin rich skin.

03:39 This picture here shows you a 70 year old female African patient and a white patient, and you can obviously see the difference in photoaging between these two.

03:50 And this is all due to the fact that Africans have got darker skin with more melanin, more melanosomes, and of course, more photoprotection.

04:01 The other advantage is the lower risk of skin cancer that you find in patients with dark skin. The disadvantage, though, is the fact that when you have more melanin and an increased number of melanosomes, you tend to get a greater risk of pigmentation alteration. And this you tend to see after inflammation, something that we called we call post-inflammatory hyperpigmentation.

04:30 There's also a higher risk for vitamin D deficiency, which leads to reduced UVB light penetration and reduced vitamin D production.

04:40 We're moving on now to the third difference, which is focusing on the differences in the dermis The dark skin has got thick and more compact dermis compared to lighter skin, where it's thinner and less compact.

04:54 The papillary and reticular layers, they are less distinct, whereas in light skin the papillary and reticular layers are more distinct.

05:03 So the following are some of the main differences between dark skin and light skin, as you can see on the slide.

05:11 I want to touch on the fibroblasts in dark skin.

05:15 There's numerous large and multinucleated fibroblasts, whereas in light skin there are very few fibroblasts.

05:24 Now, again homing down on the fibroblasts.

05:27 These differences in fibroblasts are thought to be a main factor in keloid formation in dark skin. In addition to genetics and other epigenetic factors, the other factors for keloid formation include decreased collagenase and a higher number of melanosomes in dark skin, as we have mentioned, this is a gentleman who developed a keloids after acne.

05:53 And this is how sometimes black skin heals heals with keloids and scars.

05:59 However, if you compare with light skinned patients acne, you can see the picture on the left. The patient had acne and healed beautifully after the inflammation, and this is the advantage of having less melanin.

06:15 If we move on now to head differences, what are some of the head differences between melanin rich and melanin poor skin types? So if we look at the general classification of hair of in the following groups the Asians, Caucasians and Africans.

06:33 This is a lovely table depicting the main differences in terms of morphology, the growth rate and density.

06:42 African patients tend to have slightly higher than Asian in terms of head density, but the Asians have got the lowest head density.

06:53 And of course, if you look at the cross-section of hair, the shape is different. Looking at the round and uniform in Asian hair, it's overall in Caucasian hair and flattened in African hair.

07:05 So what are the classifications of black hair types? This is a lovely study that was undertaken by Lawson.

07:13 Looking at the different hair types from type one to type eight.

07:18 Type eight being the most curly and coily type of hair compared to type one which is straight. Again, focusing on African hair, it tends to be curly with narrow angles of twists. It's got a thinner cuticle layer, and these two features make it more prone to structural damage and breakage as well as the formation of complex knots and a high prevalence of longitudinal splits.

07:53 So the curly shape of africanum makes it difficult for sebum to travel from the scalp down the hair shaft. As you can imagine, if you have a straight coil, it's easy for fluid to go through compared to something that is coily, where it has to try and navigate angles and crevices.

08:12 So the hair tends to be relatively dry compared to the other skin types.

08:19 So what are some of the implications of having a natural curly curly African hair? Well, a condition called pseudofolliculitis barbae an acne killer, Dallas nuchae is actually caused by the fact that Africans have curly hair, and that is a condition that we see quite commonly amongst African patients.