Fungi are recycling agents, helping to decompose dead material e.g. plants and animals, to put the nutrients back into the soil. Some fungi feed off living material, causing disease to plants (dutch elm disease in trees) and animals. Fungi can cause diseases such as; athlete's foot, thrush and ringworm. Fungi may sometimes cause serious infections in people who are especially susceptible to infections because their immune system is damaged. We also feel ill because of our body's response to infection. See the Immune System section for more details.