It is also known as chloasma or pregnancy mask when it happens during pregnancy. The dark patches usually appear on the face.
They are darker than the normal skin color and may occur on the cheeks, forehead, bridge of the nose, chin, upper lip, neck, forearm or other areas of the body frequently exposed to the sun.
They are not caused by infections or allergies and are non-contagious. They are not carcinogenic in nature.
It is more frequent in women but may occur in men occasionally. 90% of Melasma cases appear in women.
Darker-skinned people are more at risk of having Melasma.
It can be inherited and can run in families. It can have a significant effect on the appearance of an individual and can cause psychological and emotional distress.
The exact cause of Melasma is not clear. However, it is believed to be due to hormonal changes, stress, sun exposure, and thyroid disease.
Thus, it can be triggered by birth control pills, hormone therapy, and pregnancy. 
Ultraviolet (UV) rays from the sun cause increased production of melanin which is called - hypermelanosis.
Thus people with Melasma are advised to wear sunscreen with a high Sun Protection Factor (SPF) and protective clothing while exposure to the sun.
It is treated with topical application of steroids and creams to lighten the patches. Treatment is aimed at reducing sun exposure and reducing the production of melanin.
Melanin is a natural pigment responsible for the color of skin, eyes, and hair. Darker skin has more melanin content, while the amount of melanin is less in lighter skin tones.
It is produced in specialized skin cells called melanocytes by the oxidation of the amino acid tyrosine involving a series of biochemical pathways.
UV radiations trigger the production of melanin which makes the skin darker.
This is because melanin tends to absorb light and protects other skin cells from damage by radiation of UV rays.
Compounds in Spirulina are known to possess properties that can help in the treatment of Melasma.
Spirulina or Anthrospira platensis is a type of blue-green algae. It is rich in various kinds of nutrients and used as a nutritional supplement. It is full of proteins and provides the body with essential amino acids.
Essential minerals like iron, selenium, calcium, magnesium, phosphorous and potassium are present in Spirulina in significant amounts.
The alga is dried and is made available in the form of powder, pills, and flakes. It grows in alkaline waters and warm climates.
While other chemically synthesized creams and ointments may pose the risk of potential side effects while treating Melasma, Spirulina has been used for generations without having any side effects.
Benefits of Spirulina For Melasma
Spirulina benefits in the treatment of Melasma in the following ways:
1. It contains Several Anti-Melanogenic Compounds
Spirulina contains C-phycocyanin, a type of phycobiliprotein ( a protein that is capable of capturing light) that can absorb the Ultraviolet (UV) radiations of the sun and thereby reduce the production of melanin.
It inhibits the biochemical pathways that lead to melanin synthesis by blocking the expression of the enzyme tyrosinase. 
Spirulina also increases the production of TNF-α (Tumor Necrosis Factor-alpha) which is known to have an inhibiting action on pigmentation. 
TNF-α is a cell signaling protein. This protein inhibits melanin production and cell signaling that leads to pigmentation. 
In addition to this, Spirulina contains various polyunsaturated fatty acids (PUFAs) like oleic acid, linoleic acid, and palmitic acid.  They play a significant role in signaling of cells.
Linoleic acid stimulates the degradation of the enzyme tyrosinase, which produces melanin.
What does this Mean? C-phycocyanin and linoleic acid in Spirulina inhibit melanin synthesis and can reduce or prevent pigmentation of the skin in Melasma cases. It also increases production of certain proteins that reduce hyperpigmentation.
2. It has Many Antioxidants
UV radiations lead to the production of free radicals and cause cell injury.
Due to more exposure to these radiations, a large number of free radicals are produced which outnumber the antioxidants in the body.
This results in oxidative stress which is responsible for DNA injury. To protect skin cells from further damage by these radicals, the body increases the production of melanin pigment.
Antioxidants can fight off these free radicals so that the body does not have to increase melanin production.
Spirulina also contains tocopherols (Vitamin E) in an active state. Vitamin E is considered a highly effective depigmenting agent and an excellent antioxidant.
What does this Mean? Antioxidants like Vitamin E, present in Spirulina can tackle the toxins that lead to the production of melanin and dark patches on the skin causing Melasma.
3. It has Anti-Inflammatory Properties
Inflammatory mediators (substances that cause inflammation) are known to enhance melanogenesis and increase melanin production. 
UV rays are capable of inducing inflammation that can even cause sunburns.
Anti-inflammatory agents can neutralize the effect of UV radiations, thereby preventing inflammation and melanin synthesis by the cells.
Spirulina has anti-inflammatory nature and inhibits the functioning of various cells and proteins that are responsible for inflammation. 
What does this Mean? Spirulina has the potential to cope with inflammation and prevent melanin formation.
These properties of Spirulina can be applied to cosmetic uses for reduction of dark patches and tanned skin in case of Melasma.
In the case of Melasma, one can benefit from the properties of Spirulina by both oral intake and topical application. 
- 4-6 tablets of Spirulina (500mg) can be taken daily.
- 1-2 teaspoons of Spirulina powder can be taken daily and can be added to soups or smoothies to overcome taste issues.
- Creams and ointments containing Spirulina can be applied, but more research is required to facilitate its commercial production for cosmetic use.
- Meanwhile, Spirulina powder can be used as face masks or peels for its topical use.
It is crucial to consult with a medical professional before beginning its utilization in any way, who will be able to prescribe the recommended form of usage and dosage depending on your condition.
It is recommended to use branded and pure products that are free from contamination by toxic substances
- If planning to use Spirulina during pregnancy or breastfeeding, kindly consult with your doctor. 
- Spirulina is not considered suitable for use by people with Phenylketonuria as they will not be able to metabolize the amino acid phenylalanine, present in Spirulina.
- Individuals with known seafood allergies should be careful and proceed with caution while using Spirulina
- Spirulina should also be avoided by persons with autoimmune diseases as it could stimulate the already overactive immune system and aggravate the condition. 
- Spirulina products can absorb the toxic substances from the water body it is grown in. So one should be cautious in purchasing the products. Branded and pure products that are produced in laboratories are recommended to avoid toxicity.
- If you are on any medications, seek medical advice before using Spirulina, as it can interfere with the working of certain drugs.
In the end
Studies prove the potential of Spirulina in preventing or treating the pigmentation of skin by inhibiting the production of melanin.
These properties can be utilized to study further, the possibility of incorporating Spirulina in creams and ointments used for treating Melasma.
However, studies showing the anti-melanogenic, antioxidant and anti-inflammatory nature of Spirulina show its efficacy.
It will surely be beneficial in counteracting or reversing the effects of Melasma on skin.
With almost no side effects, compared to other chemical-based treatments, this microalga offers highly positive and promising results for Melasma.